Vegetable problems FAQs

Some of my cabbages and other brassicas were very stunted and generally making poor growth, so I dug one up and found that the roots were thickened and distorted. Could this be club root?

The symptoms you describe are typical of an early attack of club root (Plasmodiophora brassicae). Later attacks are visible above ground as a discoloration of the leaves and wilting in hot weather. Club root is encouraged by poor drainage and acid soil, so bulky organic matter should be dug in and lime applied. Crop rotation, coupled with good weed control, reduces carry-over of the disease. A proprietary club-root powder should be dusted on to the open drills and in the planting holes; or the roots of the young plants can be dipped in a made-up paste at planting time.

The leaves of some of my brassicas are turning bluish, their growth seems to be rather poor, and they tend to wilt in warm weather. Can you explain this condition?

It seems likely that the plants have been attacked by cabbage-root fly (Delia brassicae). Dig one plant up and examine the roots and base of the stem for the presence of fly maggots. Early attacks by this pest can be prevented by dusting a soil insecticide on to the seed drills and around the transplants. Later attacks can be dealt with by applying a heavy soil drench of spray-strength pirimiphos-methyl or trichlorphon.

Some tiny, white, moth-like insects are attacking my brassicas, and the plants are becoming covered with a sticky liquid which is going mouldy. What is this pest and how do I deal with it?

This is the cabbage whitefly (Aleurodes proletella), which weakens the plants by sucking the sap and also disfigures the leaves with a sticky honeydew that supports sooty moulds. It is difficult to control because the eggs and some larval stages are resistant to most insecticides. Use a special whitefly killer such as permethrin, applying a series of sprays at intervals of 5-7 days.

When I dug up my carrots I found that the surface of many of the roots were scarred and that they were infested with small maggots. How can I prevent this trouble in future?

Carrot fly (Psila rosae) is a major pest of carrots and may also attack parsnip, parsley, and celery. Attacks generally occur in May and again in August-September. Consequently, carrots sown at the end of May and lifted in August normally escape damage. Even so, whenever sowing carrots, apply a soil insecticide to the drills. Carrots which are not to be lifted until autumn should be watered in mid-August with a spray-strength solution of pirimiphos-methyl or rrichlorphon.

Some of my onions have begun to look very sickly. The outer leaves have yellowed and wilted, and when I lifted one I found some maggots in the base. Is this onion fly?

Yes. Onion fly (Delia antiqua) is one of the most damaging of onion pests and the crop should be protected from attack by applying a soil insecticide when sowing or transplanting onions. Repeat the treatment a few weeks later.

Some of my onions have started to die off. The leaves are yellowing and the young bulbs are rotting and developing a white fluffy growth. How can I prevent this trouble in future?

Your onions have been attacked by white rot caused by the soil-borne fungus Sclerotium cepiuorum. Guard against future attacks by moving the onions to a fresh site each year. The seed drills and planting holes should also be dressed with a calomel (mercurous chloride) dust.

For several years I have been growing peas successfully in the same area of my garden, but this year many of the plants are yellowing and wilting. What is the trouble?

Your peas are almost certainly suffering from a foot rot or wilt caused by a soil-borne fungus (Fusarium). Populations of these disease organisms build up if peas are grown continuously on the same site for year after year. Crop rotation is the answer to your problem, but make doubly sure by using a captan-based seed dressing. 975

The foliage of my broad beans is becoming covered with small chocolate-coloured spots. Is this some sort of disease?

The symptoms you describe are typical of the early stage of chocolate-spot disease (Botiytis fabae). This type of infection seems to have little effect on cropping, but in a wet spring the disease can cause whole areas of the leaves to rot. Improving the soil so as to give good plant growth reduces the risk of attack, as does the control of blackfly. In gardens where the disease is a regular problem, however, the young plants should be sprayed with a copper fungicide.

Until recently my sweet corn plants looked perfectly healthy, but now large, white, lumpy growths have appeared on the ears and stalks of some of the plants. Cutting a gall open, I found that it was filled with a black, greasy mess. What caused this trouble?

Your sweet corn has become infected with maize smut (Ustilago maydis), and the white galls are filled with the black spores of this fungus. Remove and burn the galls before they open and release the spores; burn any infected debris, and do not grow sweet corn in the same place for several years.

A white powdery deposit has begun to appear on the leaves and stems of my cucumbers and marrows. Is this powdery mildew and, if so, what action should I take?

Clearly your plants have been attacked by cucumber powdery mildew (Sphaerotheca fuliginea), which also infects marrows. If this disease is left unchecked the plants will suffer badly and the cropping will be greatly reduced. Start a programme of repeated sprays at 10- to 14-day intervals, using a fungicide based on benomyl, bupirimate, or thiophanate-methyl; also, ensure that the plants are kept well watered.

Some of my lettuces, which were just beginning to heart, have suddenly wilted and collapsed. I find that the tap roots have been cut through just below soil level, but I can find no sign of slugs or other pests. What has happened?

Your lettuces have been damaged by cutworms. These are the large, dingy-coloured caterpillars of various moths which live in the surface soil: check the soil near adjacent, healthy plants and you will probably be able to find and destroy the culprits. Protect against future attack by applying a soil drench of spray-strength pirimiphosmethyl or trichlorphon. 979

When lifting my parsnips late this autumn I found that many of the roots had a reddish-brown rot of the shoulder tissue. Can you identify this disease and advise how I can prevent the trouble in future?

Your parsnips have been affected by parsnip canker (usually caused by the fungus Intersonilia pastinaceae), a troublesome and widespread disease. Crop rotation reduces the risk of attack, while improving the soil by the addition of bulky organic matter such as compost, peat, or composted bark also helps. Next year, try growing one of the many canker-resistant varieties introduced in recent years, such as ‘Avonresister’.

One of my marrow plants is much smaller than the rest and its leaves are puckered and yellowed in patches. Is this due to some pest or disease?

The stunting and mottling indicates an infection of cucumber mosaic, which produces similar effects on cucumbers. There is no cure, and the disease is likely to spread by aphids to adjacent healthy plants. So dig up and destroy the affected plant at once. As this disease is extremely common it is good policy to start with more plants than you really need to allow for possible losses.

The leaves of my peas and broad beans have had semi-circular notches cut out of the margins. What pest is responsible for this damage?

The pest involved is the pea-and-bean weevil (Sitona lineata). This small beetle lives in the soil and feeds only at night. Fortunately the damage usually has little effect on cropping.

Following recent wet weather, many of the lower leaves of my potato plants have blackened and are rotting away. What causes this rot?

Your potatoes have become infected with potato blight (Phytophthora infestans). This can spread with alarming speed in damp weather, killing the whole of the haulm and infecting the tubers with a wet rot. Tomatoes can also be infected with potato blight, which kills the foliage and causes a black rot in the fruits. The answer is to spray the crop immediately with a copper fungicide and, if necessary, repeat the treatment.

When shelling my peas I found that many of the pods contained small grubs. How can I prevent this next year?

This is typical damage caused by the pea moth (Cydia nigricana).

Caterpillars hatching from eggs laid during the flowering period tunnel into the young pods and feed on the developing seeds. Early pea varieties usually escape damage, but it is good policy to spray maincrop peas with a general insecticide 7-10 days after the start of flowering. Permethrin, which is non-toxic and long-lasting, is particularly effective against these damaging pests.

Some of my tomatoes have developed a circular brown or greenish-brown sunken patch at the bottom end of the fruit. What is this caused by?

Blossom-end rot of tomatoes is caused not by disease but by irregular watering in the early stages of development of the fruit. The answer to your problem is to ensure that the soil is not allowed to dry out completely at any time. If you do this, later-developing fruit should be free of the trouble.

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