Curled up leaves on tomato plants that otherwise appear to be healthy may not be a cause for alarm. The University of Illinois Department of Crop Sciences explains that typically, leaf curl or leaf roll does not have an effect on the quality or quantity of the tomatoes. Some of the most common causes of leaf curl include a physiological condition, herbicide exposure and a virus. There are a number of steps that gardeners can take to head off leaf curl, but they must determine the source of the problem in order to take the appropriate precautions.
Physiological leaf curl
The combination of cool temperatures and rainy weather can result in tomato leaves rolling or curling up on themselves. This condition is referred to as physiological leaf curl. It can have an effect on the tomato seedlings immediately following a transplant to an outdoor setting. According to Colorado State University Cooperative Extension's master gardener Judy Sedbrook, as this issue does not prohibit plant growth or harm the fruit, it does not necessitate treatment.
There is also a type of physiological leaf roll known as "nonparasitic leaf" roll that results from a lack of water or overpruning. Typically, this leaf roll will resolve on its own after the plant has had a few days to recover from pruning or to stabilize its water supply.
Herbicide leaf curl
Tomato plants that have exposure to herbicides can exhibit indications of leaf curl. In severe cases, the leaf surface turns white and the leaf becomes brittle and thick. The most frequently occurring cause of herbicide leaf curl is 2,4-D, which is commonly used to treat crops or lawns for weeds. In order to minimize the exposure that tomato plants have to herbicides, it is important to use separate sprayers for lawns and plants. It is also important to avoid using grass clippings that have been treated with herbicide as mulch for tomato plans.
Herbicide leaf curl can cause tomatoes to be harder than normal or misshapen. However, unless the plants are exposed to herbicides in heavy doses for long periods of time, most plants will fully recover from it, particularly if you give them healthy doses of water on a regular basis.
Leaf curl virus
Sucking insects, such as aphid and sweet potato whiteflies, carry a disease referred to as 'tomato yellow leaf curl virus.' Typically this condition affects tomatoes growing in indoor settings. It can take up to three weeks for leaf curl virus symptoms to develop. During the first stages of the infection, the leaves curl upward and can appear crumpled. Later in the infection, the leaves turn yellow and curl downward. The plant growth can become stunted and even develop a growth habit similar to bush growth. Typically, flowers will not develop. When there are flowers that develop, they die off quickly. Leaf curl virus significantly compromises fruit production.
As there are no treatments for the virus, gardeners must take measures to prevent it. One of the most effective methods for prevention is choosing healthy, insect-free plants and controlling any insect infestations that do occur.