The following directory contains descriptions of common garden pests and diseases. it is divided into pests and diseases that can occur in spring,summer,autumn or winter

Spring pests and diseases

CABBAGE ROOT FLIES – These pests are not confined to vegetables; they will also attack stocks and wallflowers. The tiny white maggots eat the roots, causing leaves to wilt and turn a bluish colour. Before planting, dust the holes with a soil insecticide or, if plants are already in, apply it to the immediately around the plants before mid-spring.

CHAFER GRUBS – Bulbs, tubers and fleshy roots are attacked by these 1 ½ in long, brown-headed, white grubs. Use HCH powder or bromophos dust raked into the soil around the plants.

CRANEFLIES – the larvae, called leather jackets, of the crane fly, popularly named daddy-long-legs, eat roots and the base of stems of many plants. They are 2in long, grey-brown, plump and tough-skinned. Keep them in check by dusting the soil with HCH.

FIREBLIGHT – Many members of the rosaceous family, such as cotoneaster and pyracantha, are prone to this disease. Leaves and flowers die and turn dark brown, as though scorched. As it is very infectious, affected plants must be destroyed and the local Ministry of Agriculture office notified.

FLEA BEETLES – When the leaves of plants such as wallflowers, stocks and alyssum become pitted with small holes, these striped beetles, about ?in long, are the likely culprits. Keep them at bay by dusting plants with derris powder or HCH at an early stage of growth.

FROGHOPPERS – The white froth commonly known as cuckoo spit covers the immature froghoppers while they feed on young growth. Apply a strong water jet from a hand sprayer to dislodge them, but if they persist, spray with malathion or fenitrothion.

GREY MOULD – If stems and flowers go mouldy, especially in damp weather, they could have this disease, also known as botrytis. Apply a systematic fungicide, repeating as necessary.

LEAF MINERS – The grubs of this pest will tunnel inside the leaves of chrysanthemums, rhododendrons and lilacs, leaving unsightly white tracks. Spray with hexyl, HCH or malathion.

SCAB – Pyracantha and crab apples are attacked by scab, which shows as brown spots on leaves and rough lesions on twigs. Spray from early spring onwards with a systematic fungicide.

SILVER LEAF – This fungal infection gives the leaves of trees a silvery sheen, and they will split and turn brown. Affected branches turn brown and die back. Cut them out completely and burn them.

SLUGS AND SNAILS – Perhaps the most common of garden pests, these gastrapods cause great damage to flowers and foliage. There are slug pellets that are non-injurious to other wildlife and liquid slug killers on the market. Alternatively you can trap them in jars of beer sunk to their rims in the soil.

WIREWORMS – These aptly named creatures – they look like pieces of wire and are almost as tough – damage the roots of most flowering plants, particularly carnations and chrysanthemums. They can be controlled by dusting the soil with HCH, but perhaps the best and most natural way is to dig over the soil and expose them for birds to eat.

WOODLICE – These grey, flat, oval-bodied creatures may feed on stems, leaves and roots, but rarely do real damage. Regular cultivation and keeping the garden clear of plant debris will get rid of them as they hate disturbance and light.

WOOLY APHIDS – Cotoneaster, pyracantha and ornamental crab apples are among the shrubs and trees at risk from these aphids, easily recognised by their white woolly tufts. They puncture stems and suck the sap, and also damage the bark which splits and later becomes infected with diseases such as canker. Get rid of the insects by painting the colonies with methylated spirits.

Summer pests and diseases

ANTS
Among the many pests that bother the gardener during the summer months are ants which build nests in garden soil and around plant roots. Get rid of them with a proprietary ant killer.

CAGGAGE WHITE CATERPILLARS – The leaves of nasturtiums, wallflowers, stocks and ornamental brassicas are eaten by this green, brown or grey caterpillar. The caterpillars and egg-clusters can be picked off by hand; alternatively, spray with permethrin and dimethoate or dust with derris powder, paying particular attention to the undersides of leaves.

CAPSID BUGS – These tiny creatures are ¼ in long and may be green, brown or yellow. They attack herbaceous plants, leaving ragged holes and distorted tissue in young growth, and punctured buds, so that when the flowers open they are malformed. Spray with a systematic insecticide or malathion in spring if these pests attack regularly. Spraying after the damage is done is too late.

CLEMATIS DIE-BACK – The cause of this disease, commonly called clematis wilt, when whole plants wilt and die for no apparent reason, is imperfectly understood. If it occurs, cut the plant back to ground level and water with a systematic fungicide. Initial planting of the clematis several inches deeper than normal allows for the development of healthy shoots beneath the surface as replacements.

CUTWORMS – Plants that topple over because the stems have been eaten at soil level may have been attacked by cutworms. They are flat, soft, greeny-brown caterpillars with dark marks on each side of their 2in long bodies. Regular hoeing will expose the creatures to frosts and birds, and keeping weeds down are preventative measures; HCH dust or bromophos can be raked into the soil around established plants that are infested.

DOWNY MILDEW – There are several types of downy mildew, which is most prevalent in wet periods. Different types attack different plants, but can generally be identified by a grey mould on the undersurfaces of leaves. This can be controlled by spraying with mancozeb or copper fungicide. Systematic fungicides are of little use against downy mildews.

EARWIGS – These familiar pests, with their glossy brown bodies and pincers at the tail, damage many young leaves and flowers. HCH dust or hexyl will get rid of them, or they can be enticed into upturned pots of straw placed on top of stakes and trapped. Remove and burn the infested straw every few days.

LEAFHOPPERS – There are two species of this sap-sucking insect to watch out for, the pale yellow rose leafhopper and the green, red-striped rhododendron leafhopper. The insects feed on the undersurfaces of leaves, causing white flecks or mottling on the surface. Both species can be controlled by treating the plant with malathion, HCH or derris.

LEAF SPOT – Disfiguring, brown, round fungal blotches appear on leaves affected by leaf spot, and as they spread invade plant tissues and destroy the cells. If not controlled quickly, leaves will shrivel and plants may die. Spray with a systematic fungicide or Bordeaux mixture.

LUPIN APHIDS – These pests that appear on lupin stems are like large greenfly, but are covered with a wax coat which makes control difficult. The best way to get rid of them is to dislodge them with a strong jet of water or spray with heptenophos.

POWDERY MILDEW – The fungus appears as a powdery coating on the stems and leaves of many plants during hot weather. Spray with systematic fungicide.

RED SPIDER MITES – You may need a powerful hand lens to detect these tiny creatures on the underside of foliage, but their presence is indicated by the discoloration of leaves, which drop off prematurely. Treat them with malathion or douse the plants daily with cold water.

RUSTS – many types of plants are affected, especially roses, hollyhocks, hypericums, pelargoniums and sweet Williams. Orange-red pustules which eventually turn black appear on the undersides of leaves, and yellow spots appear on the upper surfaces. Infected leaves should be removed and burned. Treat with propicanizole or copper fungicide.

SAWFLIES – When rose leaves roll up tightly, spray them immediately with a systematic insecticide and burn infested leaves, for this is a sure sign that the larvae of the sawfly are feeding in them.

SOOTY MOULD – Sap-sucking insects such as aphids and whiteflies excrete sticky honeydew which encourages the growth of this blackish fungus. Eliminate the problem by using methods described under aphids and whiteflies.

THRIPS – It is the larvae of these minute brown or black insects, sometimes called thunder flies, that attack gladioli, roses and carnations and cause silver streaking on leaves and flowers. Use a systematic insecticide against them, and treat gladioli corms with HCH dust while they are in store.

VERTICILLIUM WILT – This fungal disease requires drastic action. Callistephus, perennial asters and dianthus, as well as some rhus, cotinus and acers may look as if they are short of water, which gives the disease its other name of sleepy disease, but they will never recover. Dig up the infected plants and destroy them, and do not put the same or any related plants in that piece of ground for several years, as the spores can survive in the soil.

WHITEFLIES – The adult whitefly is a tiny, moth-like insect commonly found in greenhouses, but also known to infest outdoor plants such as rhododendrons, honeysuckles and viburnums. The young insects feed on sap and foul the leaves with a sticky excretion called honeydew, which encourages sooty mould. Control is difficult, but spraying with permethrin-based insecticides or malathion will help.

WHITE RUST – Chrysanthemums may be hit by this fungal disease, which appears as round, yellowish-white pustules on the undersides of the leaves, and eventually causes premature death of the foliage. Spraying with propicanizole will prevent the disease occurring, but if it appears, destroy all affected plants.

Autumn trouble spots
As winter approaches, protect trees and shrubs, especially those newly planted, against strong winds with a windbreak material attached to strong stakes. Protect tender plants against frost with small-mesh plastic net, Hessian, straw or bracken. A mulch of peat, pulverised bark or garden compost will protect roots and tubers below ground.
Heavy soil which remains wet for long periods can be detrimental to plant growth, so improve drainage before any planting is done. One answer is to add large amounts of gritty sand and organic matter to open up the soil.
There are still some pests and diseases to watch out for, especially when digging – this is the best time too for removing and burning perennial weeds.

CLUB ROOT – Once this disease is in the ground it is difficult to clear. Identified by irregular swellings on the roots of wallflowers, stocks and related plants, it should not occur if you buy healthy plants. The disease is most common on wet, poorly drained soil, so improving the drainage can help. Dip the plants’ roots in a systematic fungicide solution at planting time.

HONEY FUNGUS – identified by yellowish-brown toadstools or strands like boot laces in the soil around the base of a tree or shrub, this fungus can attack any plant and is very damaging. Affected plants should be lifted and burned, but get the diagnosis confirmed by an expert before destroying valuable trees and shrubs. The ground must be sterilised with an agent such as dephenolated creosote or the soil replaced before growing anything on the site again.

STEM AND BULB EELWORMS – Herbaceous perennials and the bulbs of tulips, scillas and narcissi are attacked by these minute, wormlike creatures which are invisible to the naked eye. Infested bulbs feel soft around the neck and the foliage is stunted and sometimes splits. Always buy firm, dry bulbs. Destroy affected bulbs and plants, though root cuttings taken from perennials such as phloxes will be healthy. Do not, however, put any susceptible plants in infected ground for several years.

SWIFT MOTH CATERPILLARS – These 1-2in long caterpillars live underground and feed on fleshy roots and bulbs they are often found when herbaceous borders are dug in the autumn. Dust the soil with HCH or bromophos and suppress weeds to make the border less attractive to egg-laying females.

Winter trouble spots
Keep the garden tidy during winter. Decaying plant material will harbour pests such as slugs and woodlice, and contribute to the spread of diseases. Many pests are dormant at this time. It makes better use of your horticultural chemicals to wait and see what pests appear in spring than to spray indiscriminately with a toxic cocktail at the egg stage, that would wipe out beneficial creatures too.
Heavy snowfall on evergreens can cause them to become misshapen and their branches to break under the weight, so dislodge it as soon as possible.

CORAL SPOT – This fungal disease appears on dead or dying twigs of trees and shrubs as tiny, salmon-pink spots. It can move down into living wood causing die-back, and will attack acers, beeches, cercis and magnolias. Remove and burn the infected wood.

DAMPING OFF – This may affect seedlings which have recently germinated or have been overwintered, particularly if they were sown in unsterilised compost. Always sow in sterile compost and water all seed trays with Cheshunt compound or copper fungicide after sowing and again just as seedlings appear.

DIE-BACK – Badly pruned, insect or frost-damaged branches on roses and other woody plants may develop die-back. Remove and destroy the affected parts and treat the cut areas with a systematic fungicide.

MICE – Young shoots, seeds and seedlings in a cold frame or greenhouse, and bulbs in the garden, are a favourite diet of mice. Lay traps or keep a cat.

PEACH LEAF CURL – Ornamental prunus are attacked by this disease. When the buds burst the young leaves distort and eventually turn red, then thicken and later brown and drop off. To protect your plants, spray with Bordeaux mixture or copper fungicide during early February, and again in autumn. Collect and burn the leaves as they fall.

See also:
Environmentally friendly pest control
Chemical pest control