Fruit and vegetable diseases

Page last updated: Friday, 2 February 2018 - 12:07pm

Please note: This content may be out of date and is currently under review.

This web article describes the most common diseases of vegetables in home gardens.

Home gardeners frequently see diseases affecting their vegetables. Usually they would have seen them in previous seasons, and the symptoms look familiar.

Unfamiliar diseases could cause significant problems for our primary industries and environment if they were to become established in Western Australia.

So if you see an unusual disease please contact the Pest and Disease Information Service (PaDIS) on 1800 084 881 or

Diseases caused by fungi and bacteria

Bacterial speck

Bacterial speck is a bacterial disease and results in small, black spots on leaves, stems and fruits of tomatoes, at all stages of growth. It is most common from winter to mid spring. Copper hydroxide may give some control.


Clubroot is a fungus disease that only affects Brassicas (the broccoli family). Plants are yellowish and stunted, with large malformed ‘clubbed’ roots. Clubroot may be severe in warm weather. Avoid growing brassicas in the same area for four years and lime the soil if it is acidic.

Roots of a broccoli plant affected by the disease clubroot.  The white roots are swollen, twisted and unable to adequately take up water and nutrients.

Leaf spot diseases

There are many types of leaf spot diseases that can affect beetroot, broad beans, carrots celery, peas, potatoes (early blight) silverbeet, and tomatoes (target spot). Sometimes the leaf spots cause only slight damage, but if necessary, control with mancozeb or copper hydroxide.

Close up of plant damage caused by leaf spot disease.


Damping-off fungal diseases such as pythium may kill small seedlings of most vegetables. Seedlings die before they emerge or soon after emergence, which results in plant collapse. Damage may occur all year, mainly in wet conditions. Do not over-water and ensure that plants are not too crowded.

Downy mildew

In spring, with mild, humid weather, downy mildew fungus disease can cause greyish-white patches on the leaves of onions, which can droop from the tips. Cauliflowers, peas and lettuce may show white, downy growth on the underside of the leaves. With rhubarb, patches develop which tear to produce holes in the leaves. The fungus that causes downy mildew in a particular crop is specific to that crop. Control with mancozeb or copper hydroxide.

Downy mildew on grape vine leaf

Powdery mildew

Powdery mildew is a fungal disease. In warm, moist conditions, white patches occur on the surfaces of older leaves and leaves turn brown and shrivel. The disease is common with the cucurbit family such as cucumbers, melons, pumpkins and zucchini. It may also occur in peas and strawberries. Sulphur sprays will help to control the disease, but do not spray on hot days. Fungicides containing bicarbonate of soda also help control mildew but should be applied as soon as the disease is noticed.

Powdery mildew on grape vine leaves

Tuber diseases

Potato tubers may be infected with superficial skin diseases, such as common scab, powdery scab and rhizoctonia. Sweet potatoes may be infected by scurf. The tubers are often edible if the infected areas are cut out. Rotate crops and plant from healthy stock.

A potato tuber covered with sunken circular lesions that have flaps of skin covering the outside

White mould

White mould or sclerotinia is a fungal disease that can attack most vegetables, especially beans, celery, lettuce and the broccoli family, mainly from spring to autumn. Soft brownish water rots develop mainly on the stems, followed by a fluffy white growth and small black pebble-like bodies. White mould may stay in the soil for many years and affect following crops. Do not over-crowd or over-water plants.

Sclerotinia lesion on leaf

Wilt diseases

Fungal diseases such as fusarium, rhizoctonia and verticillium can cause wilting and death of most vegetables, by attacking roots and basal stems. Burn diseased plant remains, rotate crops and use new stakes. Some hybrid tomato varieties have resistance to fusarium.

A potato tuber cut in half revealing fungal growth inside a cavity

Viruses and mycoplasmas

There are many types of viruses and mycoplasmas that can damage most vegetables. Symptoms are usually stunting, and mottled twisted leaves. There are no pesticides that can be used to kill viruses. These are often spread by aphids, thrips or leafhoppers. Reduce viruses by controlling these insects with pesticides.

Severe viruses include cucumber mosaic virus (most vegetables), zucchini yellow mosaic virus (cucumber, pumpkins, melons and zucchini), leaf roll virus and virus X and Y (potatoes), and spotted wilt virus (capsicums, lettuce and tomatoes). Big vein mycoplasma is common on lettuce in winter and does not have an insect vector. Big bud mycoplasma attacks tomatoes

Blossom end rot

Blossom end rot is not a disease. It occurs mainly in tomatoes, capsicums and watermelons as a dry rot at the end of the fruit. It is caused mainly by a shortage of water in hot weather and some varieties are more tolerant than others. Round varieties of watermelons are less affected by this rot.

Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080