Garden Pests and Diseases of Cucurbits

Pests, Diseases and Problems of Vegetables

Cucurbits and related crops

Including: marrows, courgettes, cucumbers, squashes and pumpkins

Cucumber mosaic/Zucchini yellow mosaic virus (ZYMV)

Typical symptoms: A yellow mosaic pattern appears on leaves and the plants grow poorly; fruits are puckered and deformed. Symptoms caused by ZYMV are usually much more severe.

Prevention and treatment: There is no cure. Remove infected plants as soon as symptoms are seen and burn or dispose of diseased plants outside the garden. Where cucumber mosaic is a regular problem, grow resistant varieties. There are as yet none resistant to ZYMV.

Fruit bitter

Typical symptoms: Cucumber fruit tastes bitter, even when young.

Prevention and treatment: Do not use excessive amounts of nitrogen fertilizers and maintain an even water supply. Prevent pollination of greenhouse varieties by removing the male flowers before they open or grow varieties that produce female flowers only.

Fruiting poor

Typical symptoms: Very few or no fruit are produced.

Prevention and treatment: See Plant Disorders – Understanding the Problem

Powdery mildews (Erysiphe cichoracearum, Sphaerotheca fuliginea)

Typical symptoms: A powdery white coating appears on leaves, especially in dry weather and at the end of the season.

Prevention and treatment: See How to Treat Common Plant Diseases

Red spider mite, glasshouse (Tetranychus urticae)

Typical symptoms: Leaves are lightly mottled and tiny greenish mites can be seen on the underside, although a magnifying lens may be needed to spot them. Silken webbing may be present when infestation is in an advanced stage. Red spider mite is mainly a problem in greenhouses, but it can also occur outside in hot, dry weather.

Prevention and treatment: Mist plants with water twice a day in warm weather and use a biological control (Phytoseuilus persimilis). Also, clean the greenhouse thoroughly in autumn.

Sclerotinia (Sclerotinia sclerotiorum)

Typical symptoms: Plants rot at soil level; a white cottony mould may also be present on affected plants.

Prevention and treatment: See How to Treat Common Plant Diseases

Whitefly, glasshouse (Trialeurodes vaporariorum)

Typical symptoms: Small white flies on underside of leaves. Black sooty mould may be present on upper sides.

Prevention and treatment: Use yellow sticky traps to monitor the presence of whitefly in the greenhouse. Reduce whitefly numbers by using a portable vacuum cleaner to suck up adults disturbed by shaking the plants. If this does not work, spray with insecticidal soap. Alternatively, introduce the biological control agent Encarsia formosa as soon as the first whitefly are seen. Clean out the greenhouse thoroughly in autumn.