Problems With Curling Leaves in a Vegetable Garden

Sometimes it may seem that all the bugs, fungi and diseases in your county want your fresh, tasty vegetables as much as you do. Numerous problems afflict vegetable plants, and leaf deformation is one of the biggest signs of trouble. If your plants' leaves are rolling up, it's possible that you have a pest or disease problem that needs attention.

Aphids are tiny insects that afflict a variety of plants, including vegetable plants. Aphids gather in groups, sucking plant sap from the stems. During heavy infestations, aphid damage can drain enough fluid from the plants that the leaves begin to curl, and this is one of the first problem signs you may observe. Aphids also leave behind a sticky substance called honeydew, so if you touch the leaves and find them sticky, you likely have an aphid problem. Sooty mold sometimes develops on honeydew-soaked leaves as a secondary infection, and the honeydew attracts ants as well. Control aphids by rinsing them off of plants with a strong stream of water. Horticultural oils and insecticidal soaps can also help with control.

Occasionally, the leaves of tomato plants may roll inward, moving from the bottom to the top of the plant. No other signs of disease are present, and the tomato continues producing normally. The causes of this condition--termed physiological leaf roll--aren't well understood, according to the Pacific Northwest Extension, but current theories suggest that physiological leaf roll occurs when water evaporates from the leaves faster than the roots can replace it. Hot, dry weather and growing seasons that favor a heavy top growth both increase the likelihood of the problem. Shading plants when temperatures reach above 95 degrees F and planting resistant or determinate cultivars can prevent this problem.

Similar symptoms on potato plants are caused by a virus that causes leaves to become stiff and yellowed in addition to rolling. The symptoms may start at the top or bottom of the plant. Potato leafroll is spread by aphids or by planting infected seed potatoes. In some varieties, the potatoes themselves begin to rot. Because a virus causes potato leafroll, there is no treatment. Use only certified disease-free seed potatoes, remove any plants showing symptoms and plant cultivars with some resistance to the virus.

Curly top virus causes leaf curling, yellow leaves with purplish veins, stunted growth and reduced yields in a variety of common vegetable plants, including tomatoes, peppers, spinach, beans, cucumbers, squash, beets and cabbage. The bean leafhopper transmits the disease, becoming infected in as little as one minute of feeding, according to the New Mexico State University Cooperative Extension, at which point it spread the disease to any plant it feeds on for the rest of its life. There is no treatment for the virus, but covering young plants with netting to exclude leafhoppers may help prevent infection. Once plants are older, they are better able to resist infection.