Pests, Diseases and Problems of Vegetables

Pests, Diseases and Problems of Vegetables

(See also Pests and Diseases of Seedlings and Young Plants)


Brassicas and related crops

pests, diseases and problems of vegetables - brussels sprouts Including: Brussels sprouts, broccoli, cauliflower, cabbage, calabrese, Chinese cabbage, kale, radish, swede, turnip and Oriental greens


Blossom (pollen) beetle (Meligethes aeneus)

Typical symptoms: Heads of calabrese are grazed by these small beetles which are black and shiny.

Prevention and treatment: Protect plants with a lightweight cover like horticultural fleece. This must be done before any flower buds appear.


Bolting

Typical symptoms: Plants (especially Chinese and spring cabbage) flower prematurely.

Prevention and treatment: See Plant Disorders – Understanding the Problem


Boron deficiency

Typical symptoms: Cauliflower curds show brown patches when cut.

Prevention and treatment: See Plant Mineral Deficiencies


Cabbage root fly (Delia radicum)

Typical symptoms: Seedlings and young plants grow poorly and are easily pulled from the ground. Small white maggots eat the roots.

Prevention and treatment: Encourage natural enemies such as centipedes, ground beetles and birds. Protect plants with a lightweight cover, a cabbage rootfly mat (see Garden Pests and Diseases – Barriers and Traps) or by inter-cropping with beans. Earthing up infested plants can encourage new root growth if the plant is not already too far gone. Winter-dig the soil after an infected crop to expose pupae to birds.


Cabbage whitefly (Aleyrodes proletella)

the Cabbage Whitefly cycle


Typical symptoms: Plants become infested with tiny white flies which fly up when disturbed. Leaves may be sticky and covered with a black, sooty mould.

Prevention and treatment: Break the cycle (see Organic Gardening – Preventing Problems (Breaking the Cycle)) by removing all overwintered brassica plants before planting out new ones. Bury old plants in a trench 30cm (1ft) deep or in a compost heap. Pick off lower leaves infested with young whitefly “scales” on the underside. If the problem is severe spray with insecticidal soap, preferably on a cold day when the white-fly are less active.


Caterpillars

The caterpillars that affect brassicas are those of the small white butterfly (Pieris rapae), the large white butterfly (Pieris brassicae) and the cabbage moth (Mamestra brassicae).

Typical symptoms: Leaves have irregular holes or are stripped down to the veins. Caterpillars may be also present.

Prevention and treatment: Encourage natural enemies such as wasps and protect plants with a lightweight cover (see Garden Pests and Diseases – Barriers and Traps). Inspect unprotected plants, especially seedlings, regularly, and remove any caterpillars found. Look out particularly for caterpillars of the small white butterfly: these are well-camouflaged and greenish in colour. They tend to lie along the veins of the leaves and so are difficult to spot. Spray with Bacillus thuringiensis if hand-picking is not a practical option.


Club root (Plasmodiophora brassicae)

Typical symptoms: Plants grow poorly and may wilt and/or develop reddish-purple coloration. Roots are swollen and deformed or rotted to a slimy, smelly mess.

Prevention and treatment: Club root can survive in the soil for 20 years in the absence of a suit- able host plant, so it is worth trying to keep the ground club root-free. Never bring infected soil or plants into the garden. To make conditions less suitable, improve drainage on wet soils and lime soil to a pH of 6.5 to 7 before growing brassicas. Use as long a rotation as possible. Where club root is present, grow resistant varieties where available. Kale, sprouting broccoli and spring cabbage may crop despite infection. Raise transplants in large pots, and/or plant into a trench of clean soil to allow some roots to develop free of disease. Dig up and dispose of infected plants but do not compost them.


Crucifer downy mildew (Perenospora parasitica)

Typical symptoms: Yellow patches appear on upper surface of the leaves with mould growing below in damp weather. Seedlings may be stunted or killed.

Prevention and treatment: See How to Treat Common Plant Diseases


Crucifer powdery mildew (Erysiphe cruciferarum)

Typical symptoms: Powdery white coating found on leaves and other parts of plants may eventually spread and kill plants.

Prevention and treatment: See How to Treat Common Plant Diseases


Flea beetle (Phyllotreta spp.)

Typical symptoms: Small holes appear in the leaves of seedlings and young plants. Chinese cabbage is particularly susceptible to these small, shiny beetles and even larger plants can be eaten.

Prevention and treatment: Protect plants with a lightweight cover. Keep seedlings and young plants well watered in dry weather and, if the problem is severe, spray with derris.


Hormone weedkiller damage

Typical symptoms: Stems develop warty abnormal outgrowths.

Prevention and treatment: See Plant Disorders – Understanding the Problem


Mealy cabbage aphid (Brevicoryne brassicae)

Typical symptoms: Leaves are discoloured and distorted, with colonies of “floury” grey aphids.

Prevention and treatment: See Aphids as Garden Pests


Nitrogen deficiency

Typical symptoms: Leaves show yellow or purplish colouring and may be reduced in size; there is no root damage.

Prevention and treatment: See Plant Mineral Deficiencies


Pigeons

Typical symptoms: Leaves are pecked and torn, especially in winter.

Prevention and treatment: See General Garden Pests


Slugs

Typical symptoms: Leaves are eaten and slime trails are present.

Prevention and treatment: See Slugs and Snails – Garden Pest Control

02. February 2011 by Dave Pinkney
Categories: Pests and Diseases | Tags: , , | Comments Off on Pests, Diseases and Problems of Vegetables

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