The Teddington Gardener

Pests and Diseases – notes for a Workshop

Pests and Diseases & Disorders

Integrated Pest Management and green strategies 

 

 

Integrated Pest Management

Pests, Disease or Disorder?

Notes on –

Pests – glasshouse whitefly, mealybug, aphids, slugs & snails, glasshouse red spider mite, vine weevil, leafhopper, lily and rosemary beetles, scale insects.

Diseases – powdery mildew, blackspot, honey fungus, fireblight

Disorders – nutrient deficiencies, pH and fertilisers

 

What is IPM?

Integrated pest management, or IPM came about from studies released in the early 1960’s – it has been around for a few decades – addressing a number of issues relating to the use in both agricultural settings and home gardens. Prior to this, the application of pesticides was often the only method used to manage insects, mites and diseases. However continued reliance on pesticides gave rise to resistant pest populations and undesirable environmental effects.

Pesticides were being used without thought to their environmental impact and this realisation led to philosophical changes in the management of pests and diseases.

Although thee early studies dealt primarily with the negative impact of pesticides, it was never suggested that pesticides be eliminated completely. They are of last resort when all other management options have been eliminated.

These options included the use of ornamental plants that are less susceptible to pest and disease, with the goal of preserving natural enemies or beneficial organisms that would normally be killed by pesticide applications.

IPM also focuses on the needs of plants in landscapes and gardens, whether in sun or shade, so that they are better able to defend themselves. Healthy plants are generally able to produce more compounds to prevent extensive insect and mite damage. Plants which are either in the wrong place or are stressed by cultural practices such as watering, fertilisation, mulching and pruning have compromised defences. This opens the plant up to opportunistic attack.

IPM is an approach dealing with pests using either a single cultural, physical (mechanical), chemical or biological management strategy, or a combination of strategies.

It determines the need for monitoring pest problems – and in our gardens, the degree of pest management action taken depends on the amount of aesthetic damage that has been done. The aim of IPM strategies is not to eliminate the use of pesticides altogether but to promote its use only when needed – and that is after alternative has been considered.

Cultural pest management refers to how plants are grown and maintained in the garden and can make a difference in the types of pests present and their numbers. The attractiveness of plants to pests is affected by the species and varieties of plants, where they are planted and when they are planted, watered fertilised and harvested. The best way to prevent pest problems in the first place is to strive for good cultural practices.

A few examples –

Mowing the lawn for example – close cropping stresses the grass – mowing higher results in healthier turf. Mowing frequently so that only 1/3rd of the grass blade is revoved results in healthier turf. Grass that is consistently moved at 3’ or more will shade low-growing weeds

Watering – Water deeply but not often, especially newly planted specimens – this provides the moisture the new or recovering roots need. Watering too frequently reduces the amount of oxygen in the root ball, causing them to die.

  • Mulching
  • Plant selection and placement – sun and shade, acid, alkali…
  • Mature Plant Size
  • Soil pH and fertility – applying fertiliser
  • Crop rotation
  • Timing of planting and harvest

 

Physical Pest Management

The methods for physically removing a pest from a plant, or preventing it from reaching a plant are known as physical or mechanical pest management. These include weed pulling, cultivating, pruning out disease and insect infestations, using screens and other barriers to keep plants from reaching protected plants. These are probably the oldest management techniques. Our prehistoric ancestors will have removed lice and eggs for one another’s scalps and driving off competing animals with a club!

Handpicking is the surest method of pest control – though it is time consuming and labour intensive, whether clearing weeds or insects themselves. They may however also be stress relieving and quite satisfying…

Removing weeds

Picking off infected leaves – blackspot for example – or pruning larger sections

Shovel pruning

Picking off lily beetles and caterpillars

Squishing aphids, scrubbing scale insects, cutting out mealybug infections (with regular inspections as populations can grow very, very fast)

Trapping insects and molluscs

Using barrier to control weeds – organic mulches, black plastic, weed barrier fabric, newspaper, old carpet

Floating mulches to control insects

Mulches to control slugs and snails – including wool pellets

 

Conventional Pest Control Methods – contact and systemic control materials

Biorational control methods – generally more environmentally sound – these include bacteria, insecticidal soap, horticultural oil and botanicals.

Bacillus thurringiensis (Bt) toxins – a short residual activity and a specific range of insect pests.

Insecticidal soaps and horticultural oils are used in IPM programmes because they have a short residual activity and have minimal impact on the natural enemies of pest insects and mites. Both are contact controls. Horticultural Oils smother the insect’s breathing spores and suffocate it. They have a broad-spectrum activity and can kill live adults and overwintering stages of insect and mite pests.

In addition some horticultural oils are effective on certain foliar diseases, such as powdery mildew.

Botanical materials are derived from plant parts, are contact and degrade quickly – example have include nicotine, neem and pyrethrum. Though natural. They can still be toxic. Neem oil is a widely used insecticide acting as a repellent, anti-feedant (induces insects to stop feeding and insect growth regulator.

Pesticide resistance – alternate chemical use and implement other IPM strategies to reduce the use of pesticides.

Impact on beneficial insect populations

 

BIOLOGICAL PEST MANAGEMENT

Types of natural control – the use of natural enemies which are parasites, predators or pathogens – to manage pests.

The benefits of a diverse landscape – complex landscapes which contain a variety of plant types including flowers, shrubs and trees tend to have higher rates of natural enemies than simple landscapes – or monocultures.

Plants with flowers, including wild flowers provide mating sites for natural enemies and sites for alternative larval hosts and prey. Flowers provide essential food for natural enemies that ensures their survival and having annual and perennial plants throughout the growing season provides an abundant food source.

Why Biological Controls might not work….

Putting it all together

Assessing the needs of plants

Recognising the pests causing problems and assess whether there is a need to take action

Four courses of action – cultural, physical or mechanical, the use of pest control materials and biological controls.

Sometimes, doing nothing a much better long term strategy than simply spraying with a pesticide – pest populations may collapse naturally – natural predators might take care of that and using pesticides will disrupt them as well as the pest target. The use of pesticides should always be considered as a last resort.

 

 NOTES ON SPECIFIC PESTS –

Glasshouse whitefly

Glasshouse whitefly is a common sap-feeding pest, mainly of houseplants and greenhouse plants. They excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds.

Quick facts

Common name                   Glasshouse whitefly

Scientific name                    Trialeurodes vaporariorum

Plants affected                     Many houseplants and greenhouse plants

Main symptoms                   Sticky honeydew on foliage, black sooty moulds, small white-winged insects

Most active                            All year round

 

What is glasshouse whitefly?

Glasshouse whitefly is a sap-sucking insect pest that reduces the vigour of plants and excretes a sticky, sugary substance, called honeydew, on the leaves, stems and fruits of its host plants.

It attacks many vegetables and ornamental plants grown in greenhouses as well as houseplants. These include: cucumber, melon, tomato, peppers, Chrysanthemum, Gerbera, Pelargonium, Fuchsia, Lantana, poinsettia and Verbena. Outdoor plants can also be attacked but not to such a damaging degree. Note that whiteflies seen on brassicas, Viburnum tinus, honeysuckle, evergreen azalea and rhododendron are other species of whitefly specific to those plants.

It thrives in warm conditions, which is why it is not usually a problem on outdoor plants. Glasshouse whitefly is active all year round on houseplants and in greenhouses.

Symptoms

You may see the following symptoms:

  • It is relatively easy to see whiteflies on infested plants. When a plant is disturbed clouds of small white-winged insects, 1.5mm (about 1/16in) long, will fly up
  • You may also see flat, oval, creamy white scale-like nymphs on the underside of leaves
  • Adult whitefly and the nymphs excrete sticky honeydew on the foliage, stems and fruits, which allows the growth of black sooty moulds

Control

Due to this pest’s rapid reproductive rate and the widespread occurrence of pesticide-resistant strains, biological control often gives better results than insecticides on greenhouse plants.

Non-chemical control

Biological control

This involves introducing tiny parasitic wasps, Encarsia formosa, which attack the whitefly nymphs. The parasite is available by mail order from the suppliers of biological controls. It is important to introduce the parasite before plants are heavily infested as it cannot give instant control. Parasitised nymphs turn black so it is easy to monitor the progress of the control. As Encarsia is killed by most insecticides, avoid spraying with products other than fatty acids, urea/mineral lattice, plant extracts or plant oils (see below) prior to its introduction.

Other non-chemical controls

Hang sticky yellow sheets (widely available from garden suppliers) above or among the plants to trap adult whitefly. Glasshouse whitefly can feed and breed on weeds so good weed control inside and around the glasshouse will remove alternate host plants. Watch for signs of whitefly on new purchases as the pest is often first brought into a glasshouse on new plants. If possible quarantine new plants in order to give eggs and nymphs a chance to develop and be recognised. Good ventilation will help to check the growth of sooty moulds.

Chemical control

Frequent sprays with contact insecticides deltamethrin (e.g. Bayer Sprayday Greenfly Killer), lambda cyhalothrin (e.g. Westland Resolva Bug Killer), pyrethrins (e.g. Py Spray Garden Insect Killer, Py Bug Killer Spray, Bug Clear Gun for Fruit & Veg, Defenders Bug Killer, Growing Success Fruit & Veg Bug Killer, Growing Success Shrub & Flower Bug Killer, Vitax House Plant Pest Killer, Pyrol Bug & Larvae Killer Concentrate), plant extracts (e.g. Vitax Organic Pest & Disease Control Concentrate, Bug Clear for Fruit & Veg, Agralan Whitefly Killer), fatty acids (e.g. Bayer Organic Bug Free, Bayer Natria Bug Control, Doff Universal Bug Killer) or products which contain a blend of surfactants and nutrients (e.g. SB Plant Invigorator) can control established infestations.

Resistance to pyrethrins, deltamethrin and lambda-cyhalothrin can occur. Products containing deltamethrin and lambda-cyhalothrin can be used on edible plants listed on the label provided the label instructions on maximum dose and harvest interval are followed.

Systemic insecticides can be applied as foliar sprays or compost drenches. Systemic insecticides are absorbed into the plant tissues and are taken up by sap-sucking insects when they feed. They also usually have some contact action. There are several formulations available.

  • A compost drench containing thiocloprid (e.g. Bayer Provado Vine Weevil Killer 2) is for application to the roots of ornamental plants growing in pots or containers only
  • Foliar sprays containing thiacloprid (e.g. Bayer Provado Ultimate Bug Killer) can be sprayed on the foliage of ornamentals and some edible plants (e.g. greenhouse-grown tomatoes, peppers, aubergine and cucumber) provided the label instructions are followed.
  • Acetamiprid can be applied as a compost drench (e.g. Bug Clear Ultra Vine Weevil Killer) on container-grown ornamental plants, or as a foliar spray (e.g. Bug Clear Ultra or Bug Clear Ultra Gun) on ornamental plants only

Biology

This sap-sucking insect pest breeds rapidly and produces many generations in warm greenhouse conditions. The adults and their whitish scale-like nymphs live on the underside of the leaves where they feed on sap, weakening the plants. They lay greyish white cylindrical eggs either singly or in circles on the underside of the leaves.

Each female can lay more than 200 eggs. Males are rare and reproduction takes place without the need for fertilization. The eggs hatch into small scale-like nymphs which crawl around for a while before they begin feeding and become immobile. The nymphs are a flat, oval shape, whitish-green in colour, and just over 1mm in length when fully developed. The final nymphal stage is called a pupa and the adult whitefly eventually emerges through a slit in the dorsal surface. The length of the life cycle varies according to the temperature. At 10ºC (50ºF) the life cycle takes several months, but can be completed in about three weeks at 21ºC (70ºF). The pest can remain active during the winter in an unheated greenhouse, provided suitable host plants are present. Glasshouse whitefly does not usually survive winter out of doors.

 

Mealybug

Mealybugs are common sap-feeding pests that infest a wide range of houseplants and greenhouse plants. Mealybugs weaken plants and excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds.

Quick facts

Common name                   Mealybug

Scientific name                    Planococcus citri, Pseudococcus longispinus, P. calceolariae and others

Plants affected                     Many houseplants and greenhouse plants

Main symptoms                   Fluffy white wax, honeydew and sooty moulds

Most active                            Year round

What is mealybug?

Mealybugs are common insect pests that tend to live together in clusters in protected parts of plants, such as leaf axils, leaf sheaths, between twining stems and under loose bark. They suck sap from plants and then excrete the excess sugars as a substance called honeydew. This lands on the leaves and stems were it is often colonised by sooty moulds, giving the surfaces a blackened appearance.

Mealybugs are found mainly on greenhouse plants and houseplants, especially cacti and succulents, African violets, bougainvillea, citrus plants, fuchsia, grape vines, hoya, orchids (especially Phalaenopsis), oleander, passion flower, peach and tomato. Some other mealybug species can attack outdoor plants, such as ceanothus, laburnum, New Zealand flax and redcurrant.

Most mealybugs thrive in warm conditions, which is why they are not usually a problem on outdoor plants. Mealybugs are active all year round on houseplants and in greenhouses.

Symptoms

You may see the following symptoms:

  • Infestations are usually first noticed as a fluffy white wax produced in the leaf axils or other sheltered places on the plant. The insects or their orange-pink eggs can be found underneath this substance
  • Heavy infestations may result in an accumulation of honeydew. This makes plants sticky and encourages the growth of sooty moulds, giving leaf and stem surfaces a blackened appearance
  • Severe infestations will reduce plant vigour and stunt growth. Heavy infestations may cause premature leaf fall

Infestations are usually first noticed as a fluffy white wax produced in the leaf axils or other sheltered places on the plant, such as on this Schlumbergera (Easter cactus).

Control

Non chemical control

Female mealybugs do not fly or crawl far, so infestations are usually brought in on an infested plant. Inspect new plants carefully before putting them in a greenhouse or conservatory and, where possible, keep them in quarantine for a month or so before adding new acquisitions to an existing collection.

Dead leaves and prunings should be removed from the greenhouse as these may have mealybugs or eggs on them.

It can be simpler to dispose of heavily infested plants rather than try to eliminate mealybugs.

Biological control

A ladybird, Cryptolaemus montrouzieri, can be released into greenhouses to control mealybugs. Note that the ladybird’s larvae look like large mealybugs! Both the adult ladybirds and their larvae are able to find and eat mealybugs and their eggs in confined spaces on the plants. Parasitic wasps (Leptomastix spp.) are also available for use against this pest.

The ladybird and parasitic wasps need relatively high temperatures and so are only likely to be successful during May to September. They are susceptible to most insecticides and should therefore be used as an alternative, rather than in addition to chemical control. They are available by mail order from suppliers of biological controls.

Chemical control

Due partly to the waxy covering mealybugs are difficult to control with insecticides, affected plants should be sprayed thoroughly.

  • The systemic insecticide, thiacloprid (e.g. Provado Ultimate Bug Killer ) can be used on ornamental plants and some listed edibles such as greenhouse-grown tomatoes, peppers, cucumbers and aubergines, but not other edible plants provided manufactures instructions on application and harvest interval are followed.
  • The systemic insecticide acetamiprid (e.g. Bug Clear Ultra concentrate or Bug Clear Ultra Gun). can be used on ornamental plants only
  • Contact action insecticides deltamethrin (e.g. Bayer Sprayday Greenfly Killer and Bayer Provado Ultimate Fruit & Vegetable Bug Killer) and lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) can be used on ornamental plants and listed fruits and vegetables, provided manufactures instructions on application and harvest interval are followed.
  • Growing Success Winter Wash or Vitax Winter Tree Wash (contain plant oils) can be used on peach and grape vines in December while they are fully dormant. Scrape loose bark off grape vines before treatment in order to expose hidden mealybugs. Spread newspaper under the vine to collect the bark scrapings for disposal
  • Other organic treatments for use during the growing season include fatty acids (e.g. Bayer Organic bug free, Doff Greenfly and Blackfly Killer or Just Green Savona Concentrate) or plant oils or extracts (e.g. Organic 2-in-1 Pest and Disease Control or  Bug Clear for Fruit & Veg). These organic pesticides have a contact action and short persistence and so may require more frequent use. They can be used on all edible plants

Biology

Several species of mealybug occur in greenhouses or on houseplants. These include Pseudococcus calceolariae (Glasshouse mealybug), P. longispinus (Long tailed mealybug) and Planococcus citri (citrus mealybug).

The adult females have flattened oval-shaped soft bodies up to 4mm in length; they are sometimes pink in colour but appear whitish due to the white, waxy powder that covers their bodies. Waxy filaments project from the edges of their bodies. Some species are all female; others have small winged males, but the latter are infrequently seen.

Female mealybugs lay eggs under a white, waxy coating. Mealybug nymphs resemble the adult insects and can complete their development in about a month in mid-summer. Breeding continues throughout the year in greenhouses, but takes place at a slower rate in winter.

 

Aphids

Aphids are very common sap-sucking insects that can cause a lack of plant vigour, distorted growth and often excrete a sticky substance (honeydew) on foliage which allows the growth of sooty moulds. Some aphids transmit plant viruses which can be a problem on strawberries, raspberries, tomatoes, cucumbers, dahlias, tulips, sweet peas and many other plants.

Quick facts

Common names                 Aphids, greenfly, blackfly, plant lice

Scientific name                    Various – many species

Plants affected                     Most plants are susceptible

Main symptoms                   Poor and distorted growth, sticky                                                                                     honeydew and sooty moulds

Most active                            Spring to late summer on garden plants; all year round indoors

What are aphids?

Aphids are sap-sucking true-bugs. They range in size from 1 to 7mm (¼in or less) long. Some aphids are known as greenfly or blackfly, but there are species that are yellow, pink, white or mottled. Some species, like woolly beech aphid and woolly aphid on apple, cover themselves with a fluffy white waxy secretion and can be confused with some scale insects, mealybug or whitefly. Most aphids feed on foliage, stems and flowers but some suck sap from roots.

There are more than 500 aphid species in Britain. Some species only attack one or two plant species, but others attack a wide range of plant hosts. Almost all plants can be affected, including ornamentals, vegetables, fruits, greenhouse plants and houseplants.

Symptoms

You may see the following symptoms:

  • It is usually possible to see aphid infestations with the naked eye, and they tend to colonise shoot tips, flower buds and the underside of younger leaves
  • Aphids cause stunted growth with curled or distorted leaves. This can weaken the plant
  • Many aphids also excrete a sticky honeydew which allows the growth of black sooty moulds
  • White cast skins of aphids can accumulate on the upper surface of leaves

Aphids secrete honeydew on foliage, stems and fruits, which attracts the growth of sooty moulds. Here you can also see white cast aphid skins.

Control

Non chemical

Aphids have many natural enemies, including ladybirds, hoverfly larvae, lacewing larvae and parasitic wasps. Some of these are available for biological control of aphids in greenhouses (aphid predators). Unfortunately, out of doors, damaging aphid infestations often build up before the natural enemies are active in sufficient numbers to achieve control. Where practical infestations can be squashed by hand or knocked off with the jet of a hose.

Chemical

During the growing season there are many insecticides that can be used. It is only feasible to control aphids on plants that are small enough to be sprayed thoroughly. Aphid infestations on tall trees have to be tolerated. Always read the label use pesticides safely. Plants in flower should not be sprayed due to the danger to pollinating insects.

Pesticides based on natural compounds and/or with a physical mode of action

These pesticides are contact in action and have short persistence, so thorough spray coverage, especially to the underside of leaves, is necessary. They can be used on ornamentals and edibles up to one day before harvest.  Whilst good control can usually be gained of aphids feeding exposed on stems and leaves those protected by curled leaves are unlikely to be controlled. Products include: Pyrethrum (e.g. Py Garden Insect Killer, Bug Clear Gun for Fruit & Veg, Py Bug Killer Spray, Growing success Frit & veg Bug Killer, Growing Success Shrub & Flower Bug Killer and Pyrol Bug & Larvae Killer); Fatty acids (e.g. Bayer Organic Bug Free, Bayer Natria Bug Control, Doff Greenfly and Blackfly Killer, Doff Universal Bug Killer); Plant/fish oils (e.g. Vitax Organic Pest and Disease Control, Bug Clear for Fruit & Veg), Plant oil winter wash can be used to treat overwintering eggs on dormant deciduous fruit trees and bushes (e.g. Growing Success Winter Tree Wash or Vitax Winter Tree Wash); blend of surfactants and nutrients (e.g. SB Plant Invigorator).

Synthetic pesticides contact action

These usually have more persistence than those based on natural materials and so can give longer lasting control but will have limited effects on aphids within distorted leaves. Products include: Deltamethrin (e.g. Bayer Sprayday Greenfly Killer, Bayer Provado Ultimate Fruit & Vegetable Bug Killer) and lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) are contact insecticides that can be used on ornamental plants and listed edibles; including apple, pear, plum, raspberry, strawberry, aubergine, beans, brassicas, lettuce, peas, peppers, cucumber, courgette and tomato. Check the product instructions as there are restrictions specific to the crop on how many applications can be made and the length of time that needs to be left between spraying and harvesting (harvest interval).

Synthetic insecticides systemic action

In addition to some contact action these are absorbed into plant tissues and may have an effect on aphids hidden within distorted leaves. Thiacloprid (e.g. Bayer Provado Ultimate Bug Killer Ready To Use) can be used on ornamentals and some edibles including tomato, peppers, aubergine, courgette and cucumber in greenhouses, apple, pear, cherry, plum, almond, hazel, walnut, strawberry, bilberry, blackberry, blueberry, cranberry, gooseberry, black, red and white currants, raspberries and hybrid cane fruits, lettuce, leafy brassicas and herbs. Bayer Provado Bug Killer Concentrate 2 can be used on ornamental plants and the above mentioned glasshouse vegetables, potatoes, beetroot and Swiss chard. Read the manufacturer’s instructions regarding restrictions on the use of these products and harvest intervals. Acetamiprid (e.g. Bug Clear Ultra and Rose Clear Ultra). Bug Clear Ultra  products can be used on  apple, pear, cherry, plum,  potato, lettuce, and glasshouse tomato, pepper and aubergine, as well as ornamental plants. Read the manufacturer’s instructions regarding restrictions on the use of these products and harvest intervals.

Biology

Aphid lifecycles are variable in general for much of the year, aphid colonies consist of wingless females that give birth to live young. Winged forms develop when overcrowding, deterioration in the host plant or seasonal changes induce a move to another plant. Most aphid species overwinter as eggs but some can remain as active aphids, particularly in mild winters or on indoor plants.

Many aphids, especially those on fruits and vegetables, go through an annual cycle that involves two or more host plants. The plant on which overwintering eggs are laid is usually a tree or shrub. In the spring, the eggs hatch and the aphids feed on the young foliage. By early summer, the foliage has grown older and tougher, this combined with increasing temperatures and day-length induces winged forms of the aphid that migrate to the summer host plant. This is usually a non-woody plant with soft, succulent foliage. Some aphids, however, spend the whole year on one type of plant, although they may be active for only part of the year.

Some aphids can transmit plant viruses. This is a particular problem on soft fruits, such as strawberry and raspberry, and some vegetables such as tomatoes and plants of the cucumber/marrow family, as well as on some ornamental plants, such as dahlias, lilies, pelargoniums, tulips and sweet peas. Virus-affected plan

 

Slugs

Slugs are familiar slimy animals that often cause havoc in the garden, eating holes in leaves, stems, flowers, tubers and bulbs. There are several species of slugs that are garden pests. They can cause damage throughout the year on a wide range of plants, but seedlings and new growth on herbaceous plants in spring are most at risk.

Quick facts

Common name                   Slugs

Scientific name                    Various species, most common are species in the Milacidae, Deroceras and Arion spp.

Plants affected                     Many ornamental plants and vegetables in gardens and greenhouses

Main symptoms                   Holes in leaves, stems, flowers and potato tubers; seedlings can be killed

Most active                Year round

What are slugs?

Slugs are soft-bodied molluscs that make holes in leaves, stems, buds, flowers, roots, corms, bulbs and tubers of many plants.

Most slugs feed at night, and the slime trails, if present, can alert you to the level of activity. Damage is usually most severe during warm humid periods.

Slugs can make a meal of a wide range of vegetables and ornamental plants, especially seedlings and other soft growth. Hostas, delphiniums, dahlias, gerberas, sweet peas and tulips are regularly attacked by slugs, and it can be difficult to grow these plants if you have a big slug problem. In the vegetable garden peas, beans, lettuce, celery and potato tubers are often damaged.

Many larger slugs primarily feed on decomposing organic matter such as dead leaves dung and even dead slugs. In the compost heap they can be a valuable part of the composting process.

Symptoms

You may see the following symptoms:

  • Slugs sometimes leave behind slime trails, which can be seen as a silvery deposit on hard surface, leaves and stems
  • Slugs can make irregular holes in plant tissue with their rasping mouth parts. They can kill young seedlings by completely eating them
  • Long-keeled slugs of the Milacidae family live underground and tunnel into potato tubers and bulbs. In some gardens these slugs can damage a large proportion of the tubers of maincrop potatoes

Control

Slugs are so abundant in gardens that some damage has to be tolerated. They cannot be eradicated so targeting control measures to protect particularly vulnerable plants, such as seedlings and soft young shoots on herbaceous plants will give the best results

Non-chemical control

Biological control

A biological control (‘Nemaslug’) specific to molluscs, with no adverse effect on other types of animal, is available in the form of a microscopic nematode or eelworm that is watered into the soil. The nematodes (Phasmarhabditis hermaphrodita) enter slugs’ bodies and infect them with bacteria that cause a fatal disease.

A moist warm soil (temperatures of 5-20ºC (41-68ºF)) is required, therefore control is most effective during spring to early autumn. Best results are achieved by applying in the evening to moist but well-drained soils; control may be less successful in heavy soils, such as clay. The nematode is available from refrigerated cabinets in some garden centres, by mail order from suppliers of biological controls or direct from the company.

Other non-chemical controls

Preventive measures you can take include:

  • Transplant sturdy plantlets grown on in pots, rather than young vulnerable seedlings. Transplants can be given some protection with cloches
  • Place traps, such as scooped out half orange, grapefruit or melon skins, laid cut side down, or jars part-filled with beer and sunk into the soil near vulnerable plants. Check and empty these regularly, preferably every morning. Proprietary traps are also available from garden centres and mail order suppliers
  • Place barriers, such as copper tapes around pots or stand containers on matting impregnated with copper salts. Moisture-absorbent minerals can be placed around plants to create slug barriers .Gel repellents can also be used to create barriers around plants. These products are widely available from garden centres and mail order suppliers
  • Go out with a torch on mild evenings, especially when the weather is damp, and hand-pick slugs into a container. Take them to a field, hedgerow or patch of waste ground well away from gardens, or destroy them in hot water or a strong salt solution
  • Some birds, frogs, toads, hedgehogs, slow-worms and ground beetles eat slugs and these predators should be encouraged in gardens
  • Rake over soil and remove fallen leaves during winter so birds can eat slug eggs that have been exposed

Potatoes and slugs

The slugs that damage potatoes spend much of their time in the soil where they do not come into contact with slug pellets. The nematode treatment (see above) can be effective. Damage usually begins during August and becomes progressively worse the longer the crop is left in the ground. Early potatoes usually escape damage; maincrop potatoes should be lifted as soon as the tubers have matured if the soil is known to be slug infested. Heavy applications of farmyard manure and other composts can encourage slugs, and so inorganic fertilizers should be used where slugs are a problem.

Potatoes vary in their susceptibility to slugs. ‘Maris Piper’, ‘Cara’, ‘Arran Banner’, ‘Kirsty’,  ‘Maris Bard’, ‘Maris Peer’, ‘Kondor’, ‘Pentland Crown’ and ‘Rocket’ are frequently damaged, whereas ‘Romano’, ‘Pentland Dell’, ‘Pentland Squire’, ‘Wilja’, ‘Charlotte’, ‘Golden Wonder’, ‘Kestrel’, ‘Estima’, ‘Stemster’, ‘Sante’ and ‘Pentland Ivory’ are less susceptible.  Damaged potatoes are more vulnerable to storage rots and the crop should be sorted into sound and damaged tubers, with the latter being stored separately for early consumption.

Chemical control

Following the manufactures instructions scatter slug pellets thinly around vulnerable plants, such as seedlings, vegetables and young shoots on herbaceous plants. It is important store pellets safely and scatter them thinly as they can harm other wildlife, pets and young children if eaten in quantity.

There are two types of pellet available to the gardener; those that contain metaldehyde (e.g. Slug Clear Ultra Pellets, Bayer Bio Slug and Snail Killer, Deadfast Slug killer, Doff Slug Killer Blue Mini Pellets, Westland Eraza Slug and Snail Killer) or ferric phosphate (e.g. Growing Success Advanced Slug Killer, Bayer Natria Slug and Snail Control, Bayer Organic Slug Bait, Vitax Slug Rid, Doff Super Slug Killer, Sluggo Slug & Snail Killer). Ferric phosphate is approved for use by organic growers and is relatively non-toxic to vertebrate animals.

A liquid formulation of metaldehyde (Slug Clear) is available for watering on to ornamental plants and soil, it should not be applied to edible plants

Most plants, once established, will tolerate some slug damage and control measures can be discontinued.

Biology

Slugs vary in size from the grey field slug (Deroceras reticulatum), which is no more than 5cm (about 2in) long, to the large black slug (Arion ater), which can be 12cm (about 5in) when fully extended. Some slugs vary in colour; Arion ater can be black, orange-brown or buff coloured.

Most slugs live in or on the soil surface, but keeled slugs (Milax species) live and feed mostly in the root zone.

Slugs remain active throughout the year, unlike snails, which are dormant during autumn and winter. Warmer weather, combined with damp conditions greatly increases their activity. Slugs are most active after dark or in wet weather.

Reproduction occurs mainly in autumn and spring, when clusters of spherical, yellowish-white eggs can be found under logs, stones and pots.

Some plants less likely to be eaten by slugs (and snails)

Some herbaceous plants are less likely to be eaten by slugs and snails, these are listed below

Acanthus mollis (bear’s breeches)

Achillea filipendulina
Agapanthus hybrids and cultivars
Alchemilla mollis (lady’s mantle)

Anemone × hybrida (Japanese anemone), A. hupehensis (Japanese anemone)

Antirrhinum majus (snapdragon)

Aquilegia species

Armeria species

Aster amellus, A.× frikartii, A. novae-angliae (Michaelmas daisies)

Astilbe × arendsii
Astrantia major
Bergenia (elephant’s ears)

Centaurea dealbata, C. montana
Corydalis lutea
Cynara cardunculus (globe artichoke)

Dicentra spectabilis (bleeding heart)

Digitalis purpurea (foxglove)

Eryngium species

Euphorbia species (spurges)

Foeniculum vulgare (fennel)

Fuchsia cultivars
Gaillardia aristata
Geranium species

Geum chiloense
Hemerocallis cultivars (day lilies)

Papaver nudicaule (Iceland poppy)

Pelargonium
Phlox paniculata
Physostegia virginiana (obedient plant)

Polemonium foliosissimum
Polygonum species

Potentilla hybrids and cultivars

Pulmonaria species (lungwort)

Rudbeckia fulgida
Salvia × superba
Saxifraga × urbium (London pride)

Scabiosa caucasica (scabious)

Sedum spectabile (ice plant)

Sempervivum species (houseleeks)

Sisyrinchium species

Solidago species (golden rod)

Stachys macrantha
Tanacetum coccineum (pyrethrum)

Thalictrum aquilegiifolium
Tradescantia virginiana
Tropaeolum species (nasturtium)

Verbascum species (mullein)  

Snails –

often linked to slugs, for the kind of damage they wreak and the controls that are available –

Snails are familiar animals that can cause a lot of damage in the garden, eating holes in leaves, stems and flowers.

Quick facts                         

Common name                   Snails e.g. common garden snail

Scientific name                    Various, e.g. Cornu aspersum is a very common species

Plants affected                     Many ornamental plants and vegetables in gardens and greenhouses

Main symptoms                   Holes in foliage and flowers

Most active                            Spring to autumn

 

What are snails?

Snails are soft-bodied molluscs, with a hard shell, they can eat holes in leaves, stems and flowers of many plants.

The snail most commonly encountered in gardens is the common garden snail, Cornu aspersum. Banded snails, Cepaea species, which are a little smaller and often brightly banded yellow, white and brown, may also be numerous, but these are much less damaging to plants.

Snails are most active after dark or in wet weather, and the tell-tale slime trails, if present, can alert you to the level of activity.

Snails eat a wide range of vegetables and ornamental plants, especially seedlings and other soft growth. They are good climbers and can be found high up in some plants. Most damage is done in spring by snails feeding on seedlings, new shoots and plant crowns. Snails will also eat decomposing organic matter such as rotting leaves, dung and even dead slugs and snails.

Symptoms

You may see the following symptoms:

  • Snails sometimes leave behind slime trails, which can be seen as a silvery deposit on leaves, stems, soil and hard surfaces
  • Snails make irregular holes in plant tissues with their rasping mouthparts. Young shoots and leaves are damaged or eaten, not only at ground level but often high up

Control

Snails are often so abundant in gardens that some damage has to be tolerated. They cannot be eradicated so target control measures on protecting the more vulnerable plants, such as hostas, seedlings, vegetables and soft young shoots on herbaceous plants.

Non-chemical control

There are various measures you can take:

  • Transplant sturdy plantlets grown on in pots, rather than young vulnerable seedlings. Transplants can be given some additional protection with cloches
  • Encourage predators such as thrushes, toads, hedgehogs and ground beetles. The biological control nematode (‘Nemaslug’), Phasmarhabditis hermaphrodita, used to control slugs in the soil is unlikely to control snails, since they spend most of their time at or above soil level
  • Place traps, such as scooped-out half orange, grapefruit or melon skins, laid cut side down near vulnerable plants, or jars part-filled with beer and sunk into the soil. Check these and empty them regularly, preferably every morning. Proprietary traps and barriers are also available from garden centres and mail order suppliers
  • Place barriers, such as copper tapes around pots or stand containers on matting impregnated with copper salts. Moisture-absorbent minerals can be placed around plants to create slug barriers .Gel repellents can also be used to create barriers around plants. These products are widely available from garden centres and mail order suppliers
  • Go out with a torch on mild evenings, especially when the weather is damp, and hand-pick snails into a container. Then, either take them to a field, hedgerow or patch of waste ground well away from gardens, or destroy them in hot water or a strong salt solution
  • Turn over likely hiding places in winter to expose snails for thrushes to feed on

Chemical control

Following the manufactures instructions scatter slug pellets thinly around vulnerable plants, such as seedlings, vegetables and young shoots on herbaceous plants. It is important store pellets safely and scatter them thinly as they can harm other wildlife, pets and young children if eaten in quantity.

There are two types of pellet available to the gardener; those that contain metaldehyde (e.g. Slug Clear Ultra Pellets, Bayer Bio Slug and Snail Killer, Deadfast Slug Killer, Doff Slug Killer Blue Mini Pellets, Westland Eraza Slug and Snail Killer) or ferric phosphate (e.g. Growing Success Advanced Slug Killer, Bayer Natria Slug and Snail Control, Bayer Organic Slug Bait, Vitax Slug Rid, Doff Super Slug Killer, Sluggo Slug & Snail Killer). Ferric phosphate is approved for use by organic growers and is relatively non-toxic to vertebrate animals.

Most plants, once established, will tolerate some snail damage and control measures can be discontinued..

Biology

Snails and slugs cause similar damage and can climb, often to a considerable height, above ground level. Because of the protection provided by their shells, snails can move more freely over dry terrain than slugs.

Snails are less common than slugs where acid soils prevail and, unlike slugs, they remain dormant over winter, often clustering together under empty upturned flower pots, stones or other protected places.

Reproduction occurs mainly in autumn and spring, when clusters of spherical, yellowish-white eggs can be found under logs, stones and pots.

 

Glasshouse red spider mite

Glasshouse red spider mite is a common sap-feeding mite that causes mottled leaves and early leaf loss on greenhouse and garden plants. It is also known as the two-spotted spider mite.

Quick facts

Common name                   Glasshouse red spider mite or two-spotted spider mite

Scientific name                    Tetranychus urticae

Plants affected                     Many greenhouse and garden plants, and houseplants

Main symptoms       Mottled foliage and early leaf fall

Most active                March to October

What is glasshouse red spider mite?

Glasshouse red spider mite can be one of the most troublesome pests of greenhouse plants and houseplants. It can also attack garden plants during summer. It is a sap-sucking mite that attacks the foliage of plants, causing a mottled appearance, and in severe cases, leaf loss and plant death.

It attacks a wide range of houseplants and greenhouse plants, both ornamentals and edibles, including: vines, peach, nectarines, cucumbers, tomatoes, aubergines, peppers, Fuchsia, Pelargonium, poinsettias, orchids and Impatiens.

The host range of this pest is so wide that few plants are completely immune.

Glasshouse red spider mite thrives in warm, dry conditions, and is usually only a problem from March to October, but damage can occur at other times in a heated greenhouse. It will also cause problems outdoors in summer, especially in hot, dry weather.

Symptoms

You may see the following symptoms:

  • On leaves: Plants infested with glasshouse red spider mite show a fine pale mottling on the upper leaf surface. The underside of the leaves have many tiny yellowish green mites and white cast skins and egg shells. These are more easily seen with the aid of a x10 hand lens
  • On plants: In heavy infestations, you may see fine silk webbing on the plants, and the leaves lose most of their green colour and dry up or fall off. Heavily infested plants are severely weakened and may die

Plants infested with glasshouse red spider mite show a pale mottling and may dry up and fall off.

Control

Glasshouse red spider mite can be difficult to control as it breeds rapidly in warm conditions and some strains of the mite are resistant to some pesticides. Biological control is a viable alternative to using pesticides, it can give good control and as it avoids resistance problems and the risk of spray damage to plants.

Non-chemical control

Cultural


Remove severely infested plants from glasshouses in late summer before lower temperatures and shorter days induce the females to seek sheltered places where they will remain dormant for the winter period.  To reduce overwintering mites to a minimum, clear out plant debris, old canes, stakes and plant-ties before the spring. Empty glasshouses can be washed down thoroughly with a glasshouse disinfectant. Weeds in and around the glasshouse should be kept down as these can act as hosts for the pest. Plants grown at high temperatures in dry, overcrowded glasshouses are more liable to severe infestation. Regular syringing and spraying of plants with water and maintaining a high humidity reduce the danger of severe attacks, but will not, on its own control this pest.

Biological


The most commonly used biological control for red spider mite is a predatory mite (Phytoseiulus persimilis), originally from Chile, is now widely used in preference to pesticides.

  • The predator is about the same size as glasshouse red spider mite (0.5 mm), but they can be distinguished if examined with a hand lens
  • The predators have orange-red pear-shaped bodies, are more active than the pest, and can often be seen tapping the leaf surface with their front legs in search of prey
  • Glasshouse red spider mites are more lethargic than the predator and their body shape is rectangular. Despite its common name, they are usually yellowish-green with two dark patches. They may be entirely dark, or in the autumn they may become reddish-orange
  • The predators feed on all life stages of glasshouse red spider mite
  • The predators are dispatched as nymphs and adults which should be released in sheltered positions on infested plants
  • The predator does not control fruit tree red spider mite on apple and plum, but can be successful against glasshouse red spider mite on outdoor plants in the summer
  • The predator is susceptible to pesticides and cannot be used in conjunction with most chemical controls. The exceptions are those with very short persistence, which can be used up to a day before introduction of the predator. These include plant oils or extracts (e.g. Vitax Organic Pest and Disease Control, Bug Clear for Fruit & Veg) or fatty acids (e.g. Bayer Organic Pest Free, Doff Greenfly and Blackfly Killer, Bayer Natria Bug Control) or a blend of surfactants and nutrients (e.g. SB Plant Invigorator), which can be used to keep mite numbers in check before it is time to introduce the predator

The predator is available via mail order

Chemical control

  • Pesticides containing  acetamiprid (e.g. Bug Clear Ultra) or thiacloprid and methiocarb (e.g. Bayer Provado Ultimate Bug Killer, Aerosol)  are available for use on ornamental plants only
  • Edible plants can be sprayed with plant oils, plant extracts or fatty acids. These pesticides may require frequent applications to control the mite

Biology

Despite their common name, during the spring and summer these sap-sucking mites are yellowish-green with a pair of darker markings. Because of this, they are sometimes called the glasshouse two-spotted spider mite. They only become orange-red during the autumn and winter resting period. The mites are small, up to 1mm (less than 1/16in) long, and are just visible to the naked eye, when present in large numbers. They are usually found on the lower leaf surface, along with their spherical eggs.

Orange-red, mature female mites spend the winter months resting in cracks and crevices for example in brick walls, glasshouse frames, stakes, canes, soil and plant debris. From late March onwards they leave their resting places and start feeding and laying eggs.

The length of the life cycle depends on the temperature, but breeding can be continuous from March to October. At 10°C (50°F) the life cycle takes about 55 days, but this is reduced with increasing temperatures and at 21°C (70°F) development is completed in 12 days. Both immature and adult mites pierce plant tissues with their mouthparts and feed on cell contents. Severe damage can quickly develop in warm dry conditions which favours rapid reproduction by the mites.

 

Vine weevil

Vine weevil is an insect that can infest a wide range of ornamental plants and fruits, especially those grown in containers. Adult vine weevils eat leaves, and the grubs eat roots.

Quick facts

Common name                   Vine weevil

Scientific name                    Otiorhynchus sulcatus

Plants affected                     Ornamental plants and fruits, especially those grown in containers

Main symptoms                   Adult weevils notch leaf margins; grubs eat roots, causing plant death.

Most active                            Adult weevils: spring to late summer; grubs: summer to spring

What is vine weevil?

Vine weevil is a beetle that attacks a wide range of plants, both indoors and outdoors, but is especially damaging to plants grown in containers.

It is one of the most widespread, common and devastating garden pests. The adult weevils eat plant leaves during spring and summer, but it is the grubs that cause the most damage over autumn and winter when they feed on plant roots. This damage often results in wilting and plant death.

Plants growing in pots and containers, outdoors or under cover, are most likely to be severely damaged by vine weevil grubs. Plants growing in the open ground are less likely to be damaged, although heavy infestations of grubs can occur on strawberries, Primula, polyanthus, Sedum, Heuchera and young yew plants.

The adult beetles feed on the foliage of many herbaceous plants and shrubs, especially Rhododendron, evergreen Euonymus, Hydrangea, Epimedium, BergeniaPrimula and strawberry. Adults rarely cause enough damage to affect the vigour of plants.

There are several other species of weevil closely related to vine weevil, the adults of which cause similar damage but are less problematic as larvae.

Symptoms

You may see the following symptoms:

  • Adult weevils are approximately 9mm (about 5/16in) long and dull black with dirty yellow mark on the wing cases. They cause irregular-shaped notches of leaf margins during the summer
  • The plump c-shaped white legless grubs have light brown heads and are up to 10mm (about 3/8in) long. They are likely to be found among the roots. Plants wilt and die during autumn to spring as a result of grubs devouring the roots

Control

Gardeners with vine weevil should keep up their guard because stopping control measures after the apparent disappearance of the weevil can allow numbers to build up again.

Cultural

On mild spring or summer evenings inspect plants and walls by torchlight and pick off the adult weevils. Shake shrubs over an upturned umbrella, newspaper or similar to dislodge and collect more. In greenhouses, look under pots or on the underside of staging benches where the beetles hide during the day.

Trap adults with sticky barriers placed around pots or on greenhouse staging.

Encourage natural enemies. Vine weevils and their grubs are eaten by a variety of predators such as birds, frogs, toads, shrews, hedgehogs and predatory ground beetles.

Biological

A biological control for the larvae is available as a microscopic pathogenic nematode (Steinernema kraussei) available from suppliers of biological controls. For best results apply in August or early September when the soil temperature is warm enough for the nematode to be effective (5-20ºC/41-68ºF) and before the vine weevil grubs have grown large enough to cause serious damage.

Another nematode, Heterorhabditis megidis, is also available but is more temperature-dependent (12-20ºC/ 54-68ºF).

Both nematodes can also be applied to garden soil, but often give poor results in dry or heavy soils. They work best in open potting composts, such as peat or coir. Nematodes can be used safely on all edible and ornamental plants.

Chemical

Ornamental plants grown in containers can be treated with acetamiprid (e.g. Bug Clear Ultra Vine Weevil Killer) or thiacloprid (e.g. Bayer Provado Vine Weevil Killer 2) as a liquid drench applied to the compost. These insecticides give protection against the grubs for up to two and four months respectively; treatment in mid- to late summer will control the young larvae and prevent damage occurring later in the autumn to spring period. Neither product can be used to treat edible plants or ornamental plants growing in open soil.

Biology

Adult vine weevils cause notch like leaf damage, which can be unsightly but rarely affects plant growth. The adults are 9mm (about 5/16in) long, dull black beetles with a pear-shaped body when viewed from above. Adult weevils may be seen on the foliage at night; during the day they hide in dark places. They are slow-moving insects that cannot fly but they are excellent crawlers and climbers.

There are several other related species found in Britain which can cause similar damage to foliage as adults. Some that have recently become established include Otiorhynchus armadillo, O. crataegi and O. salicicola, cause similar damage to foliage.

Far more serious is the damage caused by the soil-dwelling larvae, which are plump, white, legless grubs up to 10mm (about 3/8in) long with pale brown heads. These eat the roots of a wide range of plants and can bore into tubers of cyclamen and begonia, and into stem bases of cacti and succulents. They can kill woody plants by gnawing away the outer tissues of the larger roots and stem bases.  Most plant losses occur during September to March, when the grubs are becoming fully grown.

All Otiorhynchus sulcatus adults are female and each can lay several hundred eggs during spring and summer – perhaps up to 1500. The eggs are brown and less than 1mm (about 1/16in) in diameter, making them very difficult to see in soil. Larger yellowish-brown spherical objects seen in potting composts are likely to be controlled-release fertiliser pellets added by the nursery that raised the plants.

 

Lily beetle

Lilies (Lilium species and hybrids), Giant lilies (Cardiocrinum species) and fritillaries (Fritillaria species) can be extensively defoliated by the common and widespread pest known as lily beetle or red lily beetle.

Quick facts

Common name                   Red lily beetle or lily beetle

Scientific name                    Lilioceris lilii

Plants affected                     Lilies (Lilium) fritillaries (Fritillaria)

Main symptoms                   Foliage is eaten by red beetles and their black excrement-coated grubs

Most active                Late March-October

What is red lily beetle?

Lily beetle and its larvae are leaf-eating pests of lilies and fritillaries. The adult beetles are very occasionally found on other plants but lilies and fritillaries are the only plants on which eggs are laid and the grubs develop. Apart from spoiling the plants’ appearance, attacks in early summer can result in undersized bulbs developing, which may not flower next year. Lily beetle has become widespread in the UK over the past three decades.

Symptoms

Most gardeners first become aware of the presence of lily beetle when their plants are stripped of foliage. Look out for;

  • Adult beetles which are 8mm long and have bright red wing cases and thorax. The head and legs are black
  • Clusters of orange-red, sausage-shaped eggs on the undersides of leaves
  • Larvae which reach 6-8mm long and are rotund, reddish brown with black heads. They are usually completely hidden under their own wet black excrement
  • Young grubs graze away the underside of leaves, resulting in white or brown dried up patches. The older grubs eat entire leaves, starting at the tips and working back to the stem, they will also feed on petals, stem and seed pods
  • Adult beetles make rounded holes in the leaves and will also feed on petals and seed pods

Non chemical control

Where only a few lilies and fritillaries are being grown, the plants should be regularly inspected from late March onwards so that adult beetles, larvae and eggs can be removed by hand. One Lilium (Lily ‘Defender Pink’) is advertised as lily beetle tolerant.

Chemical control

For extensive infestations, it may be necessary to use an insecticide, such as thiacloprid (e.g. Bayer Provado Ultimate Bug Killer), acetamiprid (e.g. Bug Clear Ultra), deltamethrin(e.g. Bayer Sprayday Greenfly Killer, Bayer Provado Ultimate Fruit & Vegetable Bug Killer) or lambda- cyhalothrin (e.g. Westland Resolva Bug Killer). Organic gardeners can use natural pyrethrum/pyrethrins (e.g. Py Spray Garden Insect Killer, Py Bug Killer spray, Bug Clear Gun for Fruit & Veg, Pyrol Bug & Larvae Killer or Growing Success Shrub and Flower Bug Killer). These products should control newly hatched larvae but are likely to be less successful against adult beetles.

Plants in flower should not be sprayed to avoid harming bees and other pollinating insects

Biology

Red lily beetle overwinters as adult beetles in soil, leaf litter and other sheltered places. This could be anywhere, not necessarily in the vicinity of lilies and fritillaries. Consequently, there is no advantage in attempting to treat the soil below lily plants. The beetles begin emerging on sunny days in late March and April when they seek out the foliage of host plants.

Eggs are laid in small batches on the underside of leaves during April to mid-summer. The eggs hatch and the larvae feed on the foliage. When fully fed, the larvae go into the soil to pupate. The next generation of adult beetles emerges from mid-summer onwards. These beetles add to the feeding damage but there is only one generation a year and these late summer adults will not mate and lay eggs until the following year.

 

Rosemary beetle

The rosemary beetle (Chrysolina americana) originates from southern Europe and has been found in Britain since the mid-1990s. The larvae and adults feed on the foliage of rosemary and related plants.

Quick facts

Common name                   Rosemary beetle

Scientific name                    Chrysolina americana


Plants affected                     Rosemary, lavender, sage, thyme and some other related plants

Main symptoms                   Foliage eaten where beetles and grubs have been feeding

Most active                            August-April; adult beetles present throughout the year

What is rosemary beetle?

Rosemary beetle is a pest that eats the foliage and flowers of various aromatic plants, such as rosemary, lavender, sage, thyme and some other related plants.

Initially rosemary beetle was found mainly in London gardens, but spread rapidly and is now widespread throughout England and Wales. It is established in Scotland, present on Northern Ireland and may be established in parts of the Republic of Ireland.

Both the adult beetles and the larvae feed on the foliage and flowers of host plants, with most of the damage occurring between late summer and the spring. Heavily infested plants can look very shabby by spring. The plants’ appearance will usually improve as new growth develops in late spring-summer.

Symptoms

Rosemary beetle and its damage are fairly easy to spot;

  • The adult beetles are shiny insects, 6-7mm long, with metallic purple and green stripes on their wing cases and thorax
  • The larvae are greyish-white with darker stripes running along their bodies; when fully grown the larvae are 8mm long
  • Both the adult beetles and the larvae feed on the leaves, which can be reduced to short stumps with greyish-brown discoloration where the damaged tissues have dried up
  • The flowers can also be damaged

Control

Non-chemical control

Hand picking can help to keep infestations below the level at which serious damage occurs. With the taller forms of rosemary and lavender, the beetles and larvae can be collected by tapping or shaking the branches over newspaper spread underneath the plant.

Chemical control

If the plants are being used for culinary purposes, the only synthetic pesticides that can be used are thiacloprid (e.g. Provado Ultimate Bug Killer Ready To Use), deltamethrin (e.g. Bayer Sprayday Greenfly Killer) and lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) Organic pesticides, such as pyrethrum (e.g. Py Spray Garden Insect Killer, Bug Clear Gun for Fruit & Veg, Pyrol Bug & Larvae Killer or Growing Success Fruit & Veg Bug Killer) can also be used on edible herbs. Pyrethrum may control the young larvae but is unlikely to deal with the adult beetles. If the herbs are to be used in food the label instructions on the pesticides must be followed, particularly the harvest interval that needs to be left between treatment and using the leaves.  

On plants grown as non-edible ornamental plants, the spray concentrate form of thiacloprid (e.g. Provado Ultimate Bug Killer concentrate) can be used.

Plants in flower should not be sprayed to avoid harming bees and other pollinating insects.

Biology

During mid-summer the pest is present on host plants as adult beetles that usually do little or no feeding. In late summer they commence feeding, mating and laying eggs. These hatch after about ten days and both adults and larvae will feed on the foliage throughout autumn to spring during periods of mild weather.

When fully fed, the larvae go into the soil to pupate. Adult rosemary beetles emerge from pupae in the soil in early summer. There is one generation a year but because the adults are long-lived, there can be some overlap between the new and old generations of adult beetles. Because of this, adult beetles can be found at almost any time of year.

 

Scale insects

Scales are limpet-like insects that feed by sucking sap from a wide range of plants, including houseplants, greenhouse plants and many fruit and ornamental plants grown outdoors. There are more than 25 species of scale insect in the UK Scale insects can weaken plants and some excrete a sticky substance (honeydew) on foliage, which allows the growth of black, sooty moulds.

Quick facts

Common name                   Scale insects

Scientific name                    Various species

Plants affected                     Many greenhouse and garden fruits and ornamental plants

Main symptom                     Scales on stems and leaves, sooty moulds on foliage

Most active                Year round

What are scale insects?

There are many different species of scale insects that attack cultivated plants. These sap-sucking insect pests can weaken the growth of a wide range of plants. Many species excrete a sticky, sugary substance, called honeydew, on the leaves and stems on which they are feeding. Some species also produce white, waxy egg masses on stems and the undersides of leaves.

A wide range of ornamental plants, fruit trees and bushes grown out of doors can be attacked. Several species of scale insects are confined to houseplants or those growing in greenhouses or other sheltered places.

Symptoms

You may see the following symptoms:

  • Scales or shell-like bumps on plant stems and the underside of leaves. These are the outer coverings of scale insect
  • Heavy infestations may result in poor growth
  • Some species of scale insect excrete honeydew, which accumulates on the upper leaf surfaces. Under damp conditions this can be colonised by a black non-parasitic fungus known as sooty mould
  • Some scale insects deposit their eggs under a covering of white waxy fibres in early summer

Control

Non-chemical control

Biological controls can be attempted during the summer in greenhouses with a parasitic wasps, Metaphycus helvolus, Encyrtus spp. and Encarsia citrina. These attack two species of scale insect, soft scale (Coccus hesperidum) and hemisperical scale (Saisettia coffeae).

The parasitic wasp is available from some mail order suppliers of biological controls.

Chemical control

The shell or scale protects the older insects from insecticides, so spraying is more effective against the newly hatched nymphs. With scales on outdoor plants there is usually one generation a year and in most species the eggs hatch in late June to July.

Scales in greenhouses or on houseplants breed throughout the year so all stages in the life cycle may be present at the same time. Scale insects can remain attached to the plant long after they are dead but new growth should be free of scales once they have been brought under control.

  • Deciduous fruit trees and roses can be treated with plant oil winter tree wash (e.g. Growing Success Winter Wash or Vitax Winter Tree Wash) on a mild dry day during December to control overwintering scale nymphs
  • Deltamethrin (e.g. Bayer Sprayday Greenfly Killer) and lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) are contact sprays that can be used on ornamental plants and a wide range of edible plants listed on the product packaging
  • Ornamental plants in leaf can be sprayed with the systemic insecticides thiacloprid (e.g. Provado Ultimate Bug Killer), which is available as a spray concentrate and a ready to use spray or acetamiprid (e.g. Bug Clear Ultra). Some formulations of these sprays can be used on some fruits, including apple, plum, gooseberry, currants, raspberry and other cane fruits, check the manufacturer’s instructions
  • Sprays based on natural substances include fatty acids (e.g. Bayer Organic Pest Control or Doff Greenfly and Blackfly Killer ) or plant oils and extracts (e.g. Growing Success Fruit & Veg Bug Killer, Bug Clear for Fruit & Veg and Vitax Organic 2 in 1 Pest & Disease Control). These pesticides have very little persistence and so may need several applications during the scale’s egg-hatching period, but they can be used on fruit trees and bushes

 Biology

More than 25 different species of scale insects are pests in the UK and these include Pulvinaria, Diaspis, Parthenolecanium, Unaspis, Coccus species and others. They suck sap from the leaves and stems of their host plants. They are mostly 1-6mm (less than ¼in) long, although wisteria scale, Eulecanium excrescens, can be up to 10mm (about ½in), and vary in shape and colour.

All species have a shell-like covering over their bodies when mature. The eggs are often laid under the protection of this shell but with the cushion scales (eg Pulvinaria species) the eggs are deposited outside the scale under a mass of white waxy fibres

The adults are sedentary but newly-hatched nymphs crawl actively over the plant surface and spread the infestation.

Scale insects in greenhouses can breed continuously throughout the year but those species that infest outdoor plants mostly have one generation a year.

Diseases

Powdery mildews

Powdery mildews are a group of related fungi which attack a wide range of plants, causing a white, dusty coating on leaves, stems and flowers.

Common name Powdery mildews

Scientific name                    Various

Plants affected                     Many plants

Main symptoms       White, dusty coating on leaves, stems and flowers

Caused by                Fungus

Timing                                   Spring onwards

What is powdery mildew?

Powdery mildew is a fungal disease of the foliage, stems and occasionally flowers and fruit where a superficial fungal growth covers the surface of the plant.

Very many common edible and ornamental garden plants are affected including apple, blackcurrant, gooseberry, grapes, crucifers, courgettes, marrows, cucumbers, peas, grasses (the powdery mildew fungi are major pathogens of cereal crops), Acanthus, delphiniums, phlox, many ornamentals in the daisy family, Lonicera (honeysuckle), rhododendrons and azaleas, roses and Quercus robur (English oak).

Powdery mildews usually have narrow host ranges comprising of just a few related plants. For example, the powdery mildew affecting peas is a different species from the one attacking apples.

Symptoms

You may see the following symptoms:

  • White, powdery spreading patches of fungus on upper or lower leaf surfaces, flowers and fruit
  • Tissues sometimes become stunted or distorted, such as leaves affected by rose powdery mildew
  • In many cases the infected tissues show little reaction to infection in the early stages, but in a few specific cases, for example on Rhamnus, the infection provokes a strong colour change in the infected parts, which turn dark brown
  • Sometimes the fungal growth is light and difficult to see despite discolouration of the plant tissues, e.g. on the undersurface of rhododendron leaves

Control

Non-chemical control

Destroying fallen infected leaves in autumn will reduce the amount of infectious spores next spring. Mulching and watering reduces water stress and helps make plants less prone to infection. Promptly pruning out infected shoots will reduce subsequent infection.

Most powdery mildew fungi have a host range restricted to a relatively few, related plants, but these can include wild relatives which can be sources of infection, e.g. wild crab apples may be sources of infection for apple orchards.

Seed producers sometimes offer powdery mildew-resistant cultivars of both vegetables and ornamental plants, check catalogues for details.

Chemical control

Because most of the growth of powdery mildews is found on the plant surface they are easily targeted with fungicides.

Edibles and ornamentals: Myclobutanil (Bayer Garden Systhane Fungus Fighter concentrate*) can be used on ornamentals, apples, pears, gooseberries and blackcurrants.

Ornamentals only: Myclobutanil (Bayer Garden Fungus Fighter Disease Control*, Doff Systemic Fungus Control and various other products, all as ready-to-use sprays); tebuconazole (Bayer Garden Multirose Concentrate 2 and Bayer Garden Fungus Fighter); Tebuconazole and Trifloxystrobin (Bayer Garden Fungus Fighter Plus) and triticonazole (Scotts Fungus Clear Ultra) can be used on ornamentals. Some formulations of myclobutanil, tebuconazole and triticonazole contain insecticides to control pests. Avoid these unless an insect pest problem is specifically identified

Plant and fish oil blends (Vitax Organic 2 in 1*) may be used on all plants.

*NB: The following products are being withdrawn:

Myclobutanil (Bayer Garden Systhane Fungus Fighter concentrate and Bayer Garden Fungus Fighter Disease Control). These products cannot be sold after the 30th November 2015 and remaining stocks must be used or disposed of before the 30th November 2016

Biology

Powdery mildew fungi produce microscopic air-borne dispersal spores from the fungal growth on the plant surface. These have an unusually high water content, enabling them to infect under drier conditions than most other fungal pathogens. Powdery mildews therefore tend to be associated with water stress.

The majority of the growth of most powdery mildews is found on the plant surface. The fungus sends feeding structures into the surface cells, greatly reducing the vigour of the plant. The growth of a few powdery mildew species (e.g. that affecting hazel) is found deeper in the plant tissues.

Powdery mildews either spend the winter as dormant infections on green tissues, or as resting structures on fallen leaves which then release spores the following spring

Rose black spot

Rose black spot is a fungal disease of roses where purple or black spots develop on leaves, which often drop early.

Quick facts

Common name                   Rose black spot

Scientific name                    Diplocarpon rosae

Plants affected                     Roses

Main symptoms       Purple or black spots on leaves, leaves falling early

Caused by                Fungus

Timing                                   Spring onwards

What is black spot?

Black spot is the most serious disease of roses. It is caused by a fungus, Diplocarpon rosae, which infects the leaves and greatly reduces plant vigour. Expect to see leaf markings from spring, which will persist as long as the leaves remain on the plant.

The fungus is genetically very diverse and new strains arise rapidly. Unfortunately, this means that the resistance bred into new varieties usually fails to last because new strains of the fungus arise to overcome it.

Symptoms

These are variable, depending on the rose variety and the strain of the fungus.

You may see the following symptoms:

  • Typically, a rapidly enlarging purplish or black patch appears on the upper leaf surface, with diffuse and radiating strands of the fungus sometimes just visible.
  • Leaf tissues may turn yellow around the spots and the leaf often drops, even though other parts are as yet unaffected
  • At other times, the yellow colour does not appear, but infected leaves still drop
  • Sometimes, the spots remain relatively small and the leaf does not drop
  • Small, black, scabby lesions may also appear on young stems

Badly affected plants can shed almost all their leaves and their vigour is greatly reduced. The symptoms are so severe that, anecdotally, the disease has been blamed for a decline in the popularity of roses in UK gardens in recent decades.

Control

Non-chemical control

Collect and destroy fallen leaves in the autumn, or bury under a layer of mulch. Prune out all stem lesions in spring before leaves appear. These actions will help delay the onset of the disease, but are of limited value because spores are bound to blow in on wind-blown rain from elsewhere.

Popular garden varieties of hybrid teas, floribundas, climbers and patio types are usually susceptible. Gardeners may gain a few years’ respite by planting the newest varieties which claim resistance, but as discussed above, this usually does not last. Older species types are little affected.

Chemical control

Fungicides containing myclobutanil (Bayer Garden Systhane Fungus Fighter*, Bayer Garden Fungus Fighter Disease Control*, Doff Systemic Fungus Control and various other products, all as ready-to-use sprays); tebuconazole (Bayer Garden Multirose Concentrate 2); triticonazole (Scotts Fungus Clear Ultra) and Plant and Fish Oil Blends (Vitax Organic 2 in 1*) may all be used. Some formulations of myclobutanil, tebuconazole and triticonazole contain insecticides to control pests. It is advisable to alternate several products to maximise their effectiveness. Avoid products also containing insecticides unless there is also a pest problem that needs control.

*NB: The following products are being withdrawn:

Myclobutanil (Bayer Garden Systhane Fungus Fighter concentrate and Bayer Garden Fungus Fighter Disease Control). These products cannot be sold after the 30th November 2015 and remaining stocks must be used or disposed of before the 30th November 2016.

Biology

The fungus produces spores in the black spot lesions on the upper leaf surface and these spread in water to initiate new infections. Wet conditions are required for the disease to build up, but most summers in the UK are sufficiently wet. The fungus spends the winter in resting structures on fallen leaves and also in dormant infections on young stems and buds, producing spores in the spring to infect young foliage.

 

Honey fungus

Honey fungus is the common name given to several different species of fungi (Armillaria) that attack and kill the roots of many woody and perennial plants. The most characteristic symptom of honey fungus is white fungal growth between the bark and wood usually at ground level. Clumps of honey coloured toadstools sometimes appear briefly on infected stumps in autumn.

Quick facts

Common name                   Honey fungus

Scientific name                    Armillaria (several species)

Plants affected                     Many woody and herbaceous perennials

Main symptoms                   Decaying roots, white fungus between bark and wood, rhizomorphs, sudden death of plant

Caused by                            Fungus

Timing                                   Mycelium and rhizomorphs present all year, mushrooms only late-summer to autumn

What is honey fungus?

Honey fungus is the common name of several species of fungi within the genus Armillaria. Honey fungus spreads underground, attacking and killing the roots of perennial plants and then decaying the dead wood. It is the most destructive fungal disease in UK gardens.

Honey fungus can attack many woody and herbaceous perennials. No plants are completely immune, but some have very good resistance, such as Juglans nigra (black walnut) and Acer negundo (box elder).

Acer (except A. negundo), Aesculus, Betula (birch), Buddleja, Ceanothus, Cedrus, Cotoneaster, × Cuprocyparis leylandii (leyland cypress), Fagus (beech), Hydrangea, Juglans (except J. nigra), Ilex (holly), Ligustrum (privet), Magnolia, Malus (apple), Photinia, Prunus (except P. spinosus), Pyrus (pear), Quercus (except Q. cerris, Q. ilex, and Q. rubra), Rhododendron (azalea), Ribes (currant), Rosa, Salix (willow), Sorbus (except S. aria), Syringa (lilac) and Viburnum are all particularly susceptible to honey fungus.

Symptoms

Some of the symptoms you may see:

Above ground

  • Upper parts of the plant die. Sometimes suddenly during periods of hot dry weather, indicating failure of the root system; sometimes more gradually with branches dying back over several years
  • Smaller, paler-than-average leaves
  • Failure to flower or unusually heavy flowering followed by an unusually heavy crop of fruit (usually just before death)
  • Premature autumn colour
  • Cracking and bleeding of the bark at the base of the stem
  • If suitable conditions permit, mushrooms are produced in autumn from infected plant material

Below ground

  • Dead and decaying roots, with sheets of white fungus material (mycelium) between bark and wood, smelling strongly of mushrooms. This can often be detected at the collar region at ground level, and rarely spreads up the trunk under the bark for about 1m (3¼ft). This is the most characteristic symptom to confirm diagnosis
  • Rhizomorphs (see images 2, 3 and 4 below) are often difficult to detect especially for the most pathogenic species and they are particularly difficult to find in the soil

To check whether a plant is infected with honey fungus, peel away the bark at the base. Look for a white or creamy white, paper thin layer of fungal tissue (mycelium), the consistency of the skin of a mushroom, as shown here.

Control

There are no chemicals available for control of honey fungus. If honey fungus is confirmed, the only effective remedy is to excavate and destroy, by burning or landfill, all of the infected root and stump material. This will destroy the food base on which the rhizomorphs feed and they are unable to grow in the soil when detached from infected material.

Non-chemical control

To prevent honey fungus spreading to unaffected areas, a physical barrier such as a 45cm (18in) deep vertical strip of butyl rubber (pond lining) or heavy duty plastic sheet buried in the soil will block the rhizomorphs. It should protrude 2-3cm (about 1in) above soil level. Regular deep cultivation will also break up rhizomorphs and limit spread.

Avoid the most susceptible plants and instead use plants that are rarely recorded as being affected by honey fungus.

Some less affected plants include: Acer negundo, Arundinaria (and other bamboos), Buxus sempervirens, Carpinus betulus, ChaenomelesErica, Fremontodendron, Garrya, Ginkgo, Hypericum, Jasminum, Juglans nigra, Larix, Nyssa, Pittosporum, Quercus ilex (holm oak), Tamarix, and Vaccinium,

Chemical control

There are no chemical controls available

Biology

There are seven species of Armillaria in the UK. The most common species in gardens are A. mellea and A. gallica. There is a rarer occurrence of A. ostoyae and A. cepistipes. The remaining species A. tabescens, A. borealis and A. ectypa have not been found in gardens according to a survey done by RHS scientists. A. mellea and A. ostoyae are the most damaging species. A. gallica and A. cepistipes are considered to be less damaging although more research is needed to find out how destructive these species are.

The fungus spreads underground by direct contact between the roots of infected and healthy plants and also by means of black, root-like structures called rhizomorphs (often known to gardeners as ‘bootlaces’), which can spread from infected roots through soil, usually in the top 15cm (6in) but as deep as at least 45cm (18in), at up to 1m (3¼ft) per year. It is this ability to spread long distances through soil that makes honey fungus such a destructive pathogen, often attacking plants up to 30m (100ft) away from the source of infection.

Clumps of honey coloured toadstools (see images 5 and 6 above) sometimes appear briefly on infected stumps in autumn, but can be safely ignored because the spores are unimportant in the life cycle of the fungus in gardens. The absence of toadstools is no indication that the fungus is not active in the soil and many plants may be killed before toadstools appear.

  1. gallica produces large and easily visible rhizomorphs quite often found in compost heaps. As a precaution, do not use infested compost around woody plants.

 

Fireblight

Fireblight is a bacterial disease which kills the shoots of apples and pears and their ornamental relatives, giving the plant the appearance of having been scorched by fire.

Quick facts

Common name                   Fireblight

Scientific name                    Erwinia amylovora

Plants affected                     Apples, pears and related ornamentals

Main symptoms                   Blossoms wilt, slime oozing from infections, cankers

Caused by                Bacterium

Timing Late              spring until autumn

What is fireblight?

Fireblight is a disease caused by the bacterium Erwinia amylovora. Expect to see damage from late spring until autumn.

Fireblight infects only those members of the Rosaceae in the sub-family Pomoideae; apples, pears and related ornamentals including Cotoneaster, Sorbus, Crataegus (hawthorn), Photinia (syn. Stransvaesia) and Pyracantha. Fireblight does not infect stone fruits, such as plums, cherriespeaches and nectarines (Prunus spp.).

Symptoms

You may see the following symptoms:

  • Blossoms wilt and die at flowering time
  • A slimy white liquid may exude from infections in wet weather
  • Shoots shrivel and die as the infection spreads down the inner bark
  • During the short period of active spread, the outer wood is stained a foxy brown colour when the infected bark is peeled back
  • Cankers (areas of dead, sunken bark) on branches, especially where infected shoots join larger branches

Control

Non-chemical control

Prune out and burn infections promptly, peeling back the bark to reveal the brown staining and cutting back 30cm (1ft) to healthy wood in smaller branches, 60cm (2ft) in larger ones. Wipe pruning tools with disinfectant (Jeyes Fluid or methylated spirit) between cuts to avoid spreading the bacteria. Remove secondary, late blossoms before they open.

Hawthorn hedges can be a source of infection and should probably be avoided by commercial fruit growers, but have many merits and should not be rejected by gardeners on this basis.

The most susceptible fruit was the pear ‘Laxtons Superb’, but this is no longer grown or offered for sale. The ‘Saphyr’ range of Pyracantha cultivars are resistant.

Chemical control

There are no specific chemical controls for fireblight, but applications of copper fungicide for control of apple canker may give some incidental control.

Biology

The bacterium is native to North America and was accidentally introduced into the UK in 1957. It was formerly a notifiable disease but this is no longer the case in mainland UK

The bacteria overwinter in bark cankers. In warm, wet and windy weather in spring, bacteria ooze out of the cankers. Infections occur when the bacterium gains entry to the inner bark, usually via the blossoms, and it is spread by wind-blown rain and also by insects including bees.

Under favourable conditions the infections spread rapidly down the inner bark at up to 5cm (2in) per day, staining the cambium a foxy brown colour. Severely attacked trees appear to have been scorched by fire. Most years in the UK are too cold at blossom time for infections to occur and the disease is usually of relatively minor importance. A particular risk of infection occurs when trees produce a secondary, small flush of blossom later in the season when conditions are warmer.

 

Disorders

All problems that are not caused by a pest or pathogen are called disorders. Nutrient deficiencies form one discreet group and climatic problems (drought, hail, sun scorch, wind damage) another. Injury to plants from these causes is erratic and fairly unpredictable and employing common sense to avoid the effects is generally the only possible action. Frost is more predictable and its effects more avoidable. Among other common and sometimes significant disorders are those resulting from chemical or pollution injury and from mechanical injury. Yet another group embraces the problems that are manifested by abnormal growth: splitting, bolting, fasciation or spiral growth, for example. In very few cases are these types of disorders either avoidable or curable.

Nutrient Deficiencies

Deficiencies are a shortage (real or induced) of a specific plant nutrient. Avoidance by regular and correct fertiliser application is much the best solution; deficiencies of most individual chemicals can be corrected by application of specific fertilisers with a high content of the relevant substance. Beware over-fertilising however – more is rarely a benefit!

The soil chemical elements most essential to plants are the ‘Big Three’ – nitrogen, phosphorous and potassium (all required in large amounts and commonly abbreviated to N, P and K, their chemical symbols – together with calcium, magnesium and sulphur (which are required in lesser amounts. Collectively these six are called major nutrients. In addition, plants require smaller amounts of minor, or trace, elements – iron, manganese, boron, copper, molybdenum, zinc and sometimes sodium and chlorine.

If any of these elements are deficient, plants will display characteristic symptoms. Nonetheless, all isn’t necessarily easy: lack of the same element can give rise to different symptoms on different types of plants; some elements give puzzlingly similar deficiency symptoms; different elements can interact with each other to give a confusing picture; and some symptoms of nutrient deficiency can be remarkably similar to effects produced by viruses, weather, pollution or other causes!

Because we place such demands on our own gardens, and especially in the vegetable garden, the three main nutrients will almost certainly become deficient unless a routine application of a balanced fertiliser is made. In alkaline soils, almost all trace elements will be unavailable to plants.

Deficiencies of Sulphur are almost unknown in British soils while chlorine, sodium and zinc deficiencies are also uncommon and restricted to very few crops.

Nitrogen can be deficient in almost all soils, especially if they are heavily cropped and where rainfall is high. Very leafy plants, such as many types of vegetables, are especially prone to the effects of nitrogen deficiency.

Phosphorous, like nitrogen, is also often deficient in regions with high rainfall as it is readily leached from the soil. It is also commonly deficient in very acidic or very alkaline soils and in many clay soils. Most types of plant can be affected.

Potassium is often deficient in light sandy soils and also on chalky and peaty soils that have a low proportion of clay particles. Vegetable and fruit crops are particularly prone to the effects of low potassium levels.

Calcium deficiency symptoms occur most commonly on acidic peaty soils and on those acid soils that originate from rocks with low calcium content. Deficiency symptoms may also be seen on light, free draining sandy soils but are uncommon on heavy clays, limestone/chalky soils. Symptoms are most common on fruit and non-leafy vegetable crops.

Magnesium deficiency often accompanies calcium deficiency on sites such as those with light, acid, sandy soils. It is readily leached from soil so is commonly deficient in regions with high rainfall. Excessive use of potassium-containing fertilisers can also result in symptoms of magnesium deficiency.

Iron is very rarely deficient in soil but its deficiency symptoms are amongst the most commonly seen. The paradox arises because iron is the element whose availability is most affected by alkalinity. Plants growing in soils overlying chalk or limestone are most likely to exhibit deficiency symptoms – rhododendrons and camellias are amongst the types most severely affected.

Manganese may be deficient in a wide range of soil types but the effects are especially severe on highly organic soils (such as peats), wet, marshy soils and on poorly draining sands. Many different types of plants may be affected but some of the classic symptoms occur on peas and beans.

Boron is sometimes deficient on soils derived from parent rocks such as granites, which are low in boron contents, or in freely draining sands from which it is readily leached. More commonly, boron is present but unavailable, often because the soil is highly alkaline. Deficiencies symptoms can therefore arise after liming or in dry summers following wet winters or springs. The effects are most commonly seen on fruits and on many vegetable crops

Copper deficiency is usually seem in highly organic soils, such as peas ad is rare on mineral soils. Fruit plants are likely to show the most symptoms.

Molybdenum is hardly ever deficient in soils but is sometimes rendered unavailable to plants in acidic conditions. The effects are almost confined to cauliflowers and broccoli.

 

Fertilisers

Fertilisers are a means by which appreciable amounts of mineral nutrients can be added to the soil, either to prevent or correct nutrient deficiencies. Most gardening needs can be supplied and most deficiencies prevented by the use of a small number of fertilisers.

General Purpose solid fertiliser

The commonest artificial compound fertiliser available in Britain is the granular mixture called Growmore, which contains 7% of the major nutrients N, P and K and it is commonly expressed as a 7:7:7 fertiliser.

The commonest organically based fertiliser is blood, fish and bone, a blend of dried blood, finely ground bonemeal and sulphate of potash (not, of course, organic). Like all organically based fertilisers, it is of more variable composition but is approximately 5.1:5:6.5. The nitrogen from the dried blood ends to be slightly more slowly available than from the ammonium sulphate in artificial mixtures and the phosphorous is more slowly released from the bonemeal component.

General purpose liquid fertiliser

Relatively high in potassium, liquid feed is very useful during rapid summer growth, the potassium being valuable tin flower and fruit development. Therefore it should be the main fertiliser for most gardeners during the height of the season. There are several branded liquid products. They vary their relative nutrient contents and most contain additional minor and trace elements, which is an advantage since they tend to be used extensively for plants growing in soil-less composts as well as those growing in the ground. The concentrated liquid tomato fertilisers are of this type and generally have a composition of 5:5:9 derived from inorganic components. Most of those purchased in the form of soluble powders or crystals fall into this category, having nutrient ratios of about 15:15:20

Lawn fertilisers

Laws should generally be fed twice a year – in spring and in autumn – but the plants’ nutrient requirements are different at these times. A fertiliser with a relatively high nitrogen content from spring and summer is recommended, and one relatively lower in nitrogen for autumn and winter.

Rose fertilisers

Several proprietary fertilisers have been formulated specifically for feeding roses. These contain a blend of the major nutrients but with a special emphasis on potassium to encourage flower growth. Most branded products also contain additional magnesium because roses are prone to deficiency of this element. An application are early spring pruning – or at leaf break – and again after the first flush of summer flowers in late June is recommended. Although formulated for roses, these fertilisers also provide an ideal balanced feed for flowering shrubs and these can be fed at the same time.

Sequestered Iron

This is iron in an inorganic form that can be readily absorbed by plants even from fairly alkaline condition

Liquid Seaweed – Maxicrop

Natural Fertilisers made from plant extracts and seaweed. No animal products used. For the organic grower – Soil Association approved. NPK fertiliser: 5-2-5 (organic garden all purpose), 4-2-6 (organic tomato), 6-2-4 (organic lawn) Balanced, healthy nutrition for all plants, fruit crops and vegetables.

Can be used as a drench, watered into the soil or container, and as a foliar spray.

SB Plant Invigorator

http://www.sbproducts.co.uk

 

 

 

Bob Flowerdew – Simple Green Pest and Disease Control

Ten step approach

1. Healthy Plants – rarely suffer from pests and diseases as frequently or as badly as undernourished or stressed plants. This is particularly true of aphids, who do not suck sap, but puncture cell walls and allow sap to be pushed through them,. They extract the minerals and proteins but let the sugary bit through – honeydew. Aphids thus prefer high sap pressure, which they find in plants under stress. Vigorous healthy plants can endure more damage than weak ones, and recover more quickly.

  • Water stress
  • Well balances nutrients
  • Balanced air flow
  • Shortage of light
  • To give a plant more of all of this, grow less of them in the same area – thin crops, space plants out…
  1. Resistant Varieties

There are usually several options for he same garden vacancy, be it ornamental or cropping. Some may have known weaknesses which are forgiven because of other qualities or heavy cropping. Partially resistant varieties may be available but at the cost of flavour or yield. Poor flavour may be a compromise worth taking if your crop is otherwise going to waste.

There is resistance and resilience – they may be immune or be resilient and still perform adequately. All late pea crops are a race between plant, weather and mildew, so the quicker ones are more likely to succeed. Often if they can just hold out a little longer then a crop or blooming can be had before the problem becomes acute.

There are parsnips resistant to canker, lettuces to root aphids, carrots to their root fly, rust-resilient leeks, scab-free apples and blight resistant tomatoes and potatoes. Most important are clubroot resistant brassicas.

Rare or uncommon is also good – if you grow the unusual, then there are seldom any pests or diseases to bother them. Of crop plants, look at sea kale, rhubarb, Jerusalem Artichoke, corn, salsify and most aromatic herbs. If you exclude bird and wasp damage, some fruits are effectively pest fee – figs, mulberries, jostaberries, cranberries,blueberris, kiwis and more…

  1. Cunning Cultural Methods

Crop rotation – plants are more vigorous in soil that hasn’t seen them in a few years and few specific pests awaiting them. Some crops can treat one place as home, if well fed – corn, runner beans.

Cleaning your tools

Regular checks for pests and disease and quick action

Pre-winter tidy of plants going under cover and cleaning of glasshouse structures.

The use of timing – moving a crop early before the worst of the problem. Early potato varieties crop early and if planted early, avoid the worst of the problem.

If you avoid touching or sowing carrots when cow parsley is flowering, you avoid the early peak of carrot root fly. Broad beans sown in autumn and overwintered are too tough for aphids when they arrive. Autumn fruiting raspberries usually evade he maggots that may plague the summer croppers

  1. Barriers

Nets, fleece, plastic bottle cloches and pea guards – all very effective. By putting an impenetrable barrier between the problem and the plant, we defuse the situation. Blackbirds from fruit, carrot root fly from carrots, pigeons from brassicas by nets, fleeces and wire guards. They are visually intrusive though most things can be made neat – or no

Edging to beds and borders are often used for neatness, to retain turf or soil or to stop weeds encroaching, but can have a significant effect on small pests including slugs, snails and vine weevils. To them, these are large vertical walls to negotiate while also making it stand out and is prey for any passing predator. Gardeners with raised beds can add copper take, or non-setting glue to reinforce the effectiveness.

Rings of copper, or plastic bottles can be useful cloches – tubes from plastic bottles even more so – encouraging a microclimate, keeping off strong winds and reducing rain and hail damage. Being deep they deter birds and most crawling problems.

Wool pellet mulches, or crushed cocoa shell, wood ash, soot, holy leaves, baked crushed eggshells all discourage slugs.

Vine weevil and ant moats stop these troublesome pests – stand pots and containers on feet in saucers of water –floating oil makes them even more effective.

  1. Hide and Seek

Camouflage plants visually and by smell.

Red or purple coloured brassicas do not suffer the same damage as usual green forms and yellow berries often fool birds into thinking they are not ripe yet.

Intercropping, mixing crops to hide shape and smell helps, and makes it harder for infestation or infection to spread.

Surrounding hedges of rosemary, hyssop or lavender around vegetable plots can hide the scent of the vegetables

  1. Traps – physical traps for the particular pest but also sacrificial plants, which can be discarded carrying the pest with them – very useful under cover – broad beans are useful for luring red spider mite, tobacco plants for whitefly and tomatoes and potatoes for mealy bugs (spray the tobacco plants with sugar syrup before moving them to stop the whitefly fleeing.
  1. Encourage natural predators

Avoid pesticides which are indiscriminate. Provide food, water and warmth for beneficial creatures – water is the most crucial. Provide different habitats – long and short grass, damp and dry areas, water and bog. The more the better.

  1. Companion Plants

Two or more different plants grown together for the benefit of one or both. Good companion planting can be used to attract or repel pests,

  1. Biological Controls
  1. Direct Action

Killing the pests yourself, directly or indirectly, even with poisons, may sometimes be necessary. Likewise some sprays and other applications may be needed to control diseases that are otherwise hard to prevent. Prompt early action is important and observation is the key.

But when using poisons – always read the instructions and

Follow them!

From Simple Green Pest and Disease Control by Bob Flowerdew – a ten step approach…

 

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One comment

  1. Pingback: Plant tonics expertly explained and recommended – thank you ‘The Telegraph’ – with some home thoughts too … | The Teddington Gardener

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