Troubleshooter

Q The leaves on my plant have curled up and gone yellow?

A This could be due to an aphid attack. They’ll gather on the underside of leaves to suck the sap and leave behind a sticky honeydew, which attracts sooty mould. Spray with insecticidal soap, or wipe them off with a gloved hand. Greenhouse whitefly also suck plant sap, leaving honeydew residues that attract sooty mould, weaken the plant and reduce cropping.

Q What’s causing the leaves to turn mottled and brittle?

A This sounds like mosaic virus, which causes leaves to become thickened, brittle and easily broken from the plant. Plants grow smaller with reduced cropping. Aphids and leafhoppers spread the virus from plant to plant, and the best solution is to destroy diseased plants and any weeds that might harbour the virus.

Q What’s eaten holes in the leaves?

A Watch out for the cucumber beetle – an attractive yellowish green beetle with either spots or stripes on their backs, about 7mm (¼in) long. Pick them off by hand when you see them. Cover outdoor plants with a cloche to keep them off, until the plants flower.

Q Why are my plants suffering from mildew?

A Powdery mildew is caused by fungal spores germinating on leaf surfaces when humidity is high and creating telltale white-grey splotches on leaf surfaces and fruits. Downy mildew is caused by fungus too with leaves showing yellow-brown spots on upper leaf surfaces and greyish powder on the undersides. For both, improve air circulation and don’t let the compost dry out.

Q How can I stop the cucumbers going soft and mouldy?

A Bacterial leaf spot can infect the foliage and fruit, causing cucumbers to rot on the plant. Fungal diseases such as grey mould caused by botrytis are prevalent in humid conditions too. Increase ventilation and remove affected fruit and foliage straight away. Leaf spot (anthracnose) causes brown spots with a yellow margin on leaves and fruit. Give indoor plants more ventilation and remove infected material to prevent spread.

Q Why are my cucumber plants dying off at soil level?

A Cutworms are grey grubs that live just under the soil and will eat stems, roots and leaves. Place a 10cm (4in) paper collar around the stem to prevent the problem and sprinkle wood ash around the base of plants. If the soil is wet and cold, your plant stems might be rotting at the base.