Pests and Diseases Affecting the Kitchen Garden

Aphids (greenfly/blackfly, currant-leaf-blister aphid, root aphids)

Tiny insects 2mm (1/8in) long, green, black, pink, grey, blue-grey, cream. Found in great numbers on undersides of youngest leaves and tips of shoots, which become curled and discoloured as the result of feeding; new growth is severely stunted. Root aphids mostly found on roots of lettuce. Feed by sucking sap from plant with pointed, stylet-like mouthparts. Hatch from over-wintering eggs in early spring, cast skins several times as they grow, and one or two produce a winged adult form, the last generation of which lays eggs to over-winter. The wingless forms are all female and produce voting aphids asexually. Spray in winter with tar oil winter wash, or with bioresmethrin, derris or malathion in spring and summer.

Big-bud mite (blackcurrants)

big-bud mite in blackcurrants

Migrates in mid-spring to healthy buds; difficult to control, but some effect obtained by spraying with lime-sulphur when flower clusters look like miniature bunches of grapes. Remove and destroy swollen buds.

Blackfy, see Aphids

Blight (potato and tomato)

A fungus disease which produces dark brown, later black, blotches and spots on leaves and stems, and brown patches in the flesh of tubers; sunken areas in the skin indicate them. Most severe infections during wet summers, especially in warm weather. Apply protective sprays containing copper or zineb early in mid-summer and then every two to three weeks until autumn. Destroy infected haulm and tubers when crop harvested.

Cabbage root fly (all brassicas)

Tiny white maggots feed on roots of seedlings and young plants, causing swelling and malformation. First brood appears late in mid-spring, second one late in early summer, sometimes a third in the middle of late summer. Eggs are laid by adult flies in soil near plant roots; maggots pupate in soil over-winter. Surround young plants with 15cm (6in) diameter black plastic sheet or plastic foam discs placed on soil, to prevent egg laying or treat soil with bromophos at planting time.

Cabbage white butterfly and cabbage moth (all leafy brassicas)

Yellowish-green and black, or brown or green caterpillars, up to 2.5cm (1in) long when fully grown, feed on outer leaves and hearts. Hatch from eggs laid on leaves in spring and become chrysalids after four weeks. Second, third and fourth generations may occur, feeding until late autumn. Handpick caterpillars; crush eggs on leaves or dust leaves with derris.

Capsid Green, fast-moving creatures, like greenfly, but much larger. Feed in a similar way, but cause much worse damage. Leaves with pinprick holes, later tattered; growth severely stunted, flowers one-sided. Spray plant and soil with dimethoate.

Carrot-fly (carrots, celery, parsley, parsnip)

Tiny white maggots tunnel into roots. Eggs laid in soil by adults in mid-spring; second brood of maggots appears in late summer and sometimes a third in autumn. Sow main-crop carrots at end of late spring, very thinly. Apply diazinon to soil.

Caterpillars

Various colours and sizes; feed on leaves. Handpick; treat with derris or fenitrothion. Celery leafly (celeriac, celery, parsley, parsnip) Eggs laid in leaves by adults, spring to early summer. Maggots hatch to iced on internal leaf tissues, causing pale brown blisters; leaves die. Second brood in late summer, third brood in mild seasons in autumn. Handpick leaves, spray with malathion in a severe attack.

Clubfoot (all brassicas)

A fungus disease carried in the soil, which infects the roots, producing swollen, contorted and rotten tissue. Seedlings and young plants can be destroyed. Leaves wilt and turn grey-green. Dip roots of transplants in a mixture of pure calomel at 60g per 0.6 litre (2oz per pint) of water or 14g (1/2oz) thiophanate-methyl before planting in sterilized compost. Destroy infected plants, including the roots; improve soil drainage and maintain pH at 7.0. Do not plant in infected ground, if possible, for at least seven years. Flea beetle (turnip, swede, beetroot, cabbage, kale, radish) Tiny blue-black, or black and yellow beetles, which hop when disturbed. Feed in spring on seedling and young leaves, making small circular holes. Adults live through winter and larvae bugs in early summer. Dust leaves with derris at once if any signs of damage seen.

Gooseberry sawfly

Caterpillars feed on leaves, leaving only skeleton of veins. Eggs laid on leaves in mid-spring; green and black caterpillars hatch from these, and a second brood can appear in early summer, with a third in late summer. Central leaves are attacked first. Handpick and spray with fenitrothion or derris if necessary.

Greenfly, see Aphids

Grey mould (Botrytis cinerea)

Fungus disease which produces grey furry mould on leaves, stems, flowers and fruits. Plant tissue rots and discolours. Worst in cool, damp conditions. Spreads rapidly in stuffy greenhouses. Handpick and destroy diseased parts; improve ventilation and raise temperature; spray with benomyl.

Leaf-hopper

Tiny insect pest which feeds by sucking sap from leaves, producing patches of cream-coloured mottling. Occurs on the underside of leaves and hops when disturbed. Wings develop as insect matures. See Aphids for control.

Mildew powdery

Fungus disease, symptoms of which are powdery white substance on leaves, stem, flowers and fruit. Infects tips of new shoots and youngest leaves first. Remove infected parts and spray with benomyl or dinocap. Mildew on lettuce is a different type called downy mildew, which needs treating with zineb.

Onion fly

Adults lay eggs in soil near young plants in late spring, and maggots hatch from eggs and enter bulbing portion of stem on which they feed. When fully grown they return to the soil, where they pupate until the following spring. Leaves of attacked plants turn yellow and wilt; bulb rots. Destroy attacked plants. Treat soil with diazinon before sowing seed or planting sets.

Potato blight, see Blight

Raspberry beetle

Ripening and ripe fruit that contain white maggots may rot. Adult beetles lay eggs in blossom in early summer (in blackberry in mid to late summer). Spray with derris when the fruit begins to colour.

Red spider mite

Minute sucking pests, only visible with a hand lens. Pale red or yellow, feed on undersurface of leaf. In bad infestations webbing is produced, and there will be many white skins, cast as the mites moult and grow. Life cycle is completed in a month, and in hot dry, conditions, they multiply very rapidly. Leaves become mottled, greyish, bronze or yellow, papery and wither. In greenhouse, they will overwinter as adults, and feed in warm conditions. Destroy badly infected plants or plant parts, and spray with bioresmethrin, malathion or dimethoate. Use biological control, the predatory mite Phytoseiulus perimilis. Alter the environment so that it is damper and less warm.

Slugs and snails

Eat irregular holes in leaves, stems, flowers and fruit. Feed by night, and hide during the day. Present all year.

Use methiocarb pellets on soil surface; surround plants with 15cm (6in) wide bands of gritty material. Sink shallow containers of sugary water, stale beer, or diluted milk in soil near crops. For underground slugs, improve soil drainage; liquid slug-killers are, unfortunately, only partially effective.

Spur blight (fungus disease)

Found on raspberry canes, as silvery elongated patches surrounding buds, which are killed, New infections occur in spring. Cut out infected canes and thin remainder. Disease usually appears amongst crowded plantings, and on canes weak from lack of food and/or water, so improve growing conditions. Spray remainder of canes with a copper-containing fungicide or with benomyl.

Tomato blight, see Potato blight

Tomato leaf-mould

Fungus disease which may appear in early summer, and be very bad by mid-summer, when it is usually first noticed. Spots on leaves spread into patches and leaves killed; spreads rapidly in conditions of high humidity and temperature and crowded planting. Remove infected part and spray with benomyl. Some varieties are resistant.

Whitefly

Minute, white, moth-like insects, whose larvae feed on the undersurface of leaves by sucking the sap from the tissue. In large numbers they severely weaken the plants and produce a sticky substance on which grows black sooty mould, making the plants extremely messy. Introduce the parasitic wasp Encarsia formosa; spray with bioresmethrin. Treat as soon as seen, otherwise very difficult to control. Destroy worst infected plants or parts of plants.

29. August 2011 by admin
Categories: Garden Management, Pest and Disease Control | Tags: , , , | Comments Off on Pests and Diseases Affecting the Kitchen Garden

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