Curling Purple Leaves on Tomato Plants

Viruses

• Viruses, such as tomato spotted wilt virus, are the most likely cause of purple, curling leaves on a tomato plant. These viruses are often spread by thrips, small, greenish-brown insects. Unfortunately, there is no cure for tomato viruses. Remove infected plants and discard them so the virus doesn't spread. Avoid planting tomatoes next to peppers and potatoes, which can also spread tomato viruses and rotate crops yearly.

Powdery Mildew

• Powdery mildew is a fungal disease most common during hot, humid weather. The main initial symptom is a white, powdery growth that coats the leaves. As the disease progresses, the leaves become blighted, curling and turning brown or purple. Plant tomatoes far enough apart so air circulates freely. The disease usually appears in late summer and causes little harm to the crop. If powdery mildew occurs in early summer, though, treat the tomato plants with a fungicide.

Plant Selection

• Many tomato varieties are bred to resist certain diseases, such as fusarium wilt or verticillium wilt. Although these tomatoes are susceptible to tomato spotted wilt virus, which causes curling purple leaves, they'll fend off other diseases better. Disease-resistant plants are especially important if you live in a hot, humid climate where plant diseases are common.

Growing Conditions

• Aphids, thrips, leafhoppers and whiteflies all spread tomato diseases. To minimize the risk of curling purple leaves caused by viruses, control insects early in the season. Use insecticidal soaps, predatory insects or pesticides. Avoid wetting the tomato plant leaves or working in the garden while it is wet, because wet leaves spread disease.