This crazy summer has had its toll on our gardens. With the wild swings in temperature and stormy, windy weather, it's not surprising to see our plants reacting in adverse ways.
Recently I have been getting many questions about weird, curling tomato leaves. Tomato plants can develop disorders that distort plants and blemish fruits. Some disorders are not caused by diseases, but are the result of cultural practices or environmental conditions.
Generally, good cultural practices that ensure consistent plant growth will reduce these types of disorders.
Leaf roll is a physical disorder of tomatoes that is associated with hot dry weather, but can occur in response to other stresses like fast growth, high production and pruning. This disorder is believed to be a strategy to conserve moisture.
Symptoms of leaf roll are:
• Leaf margins roll upward until they touch or overlap in an almost tube-like fashion.
• Affected leaves are firm and leathery to the touch.
• Lower leaves are commonly affected first.
Once leaves roll, they will not unroll even if weather conditions become cool and wet. In severe conditions the entire plant may exhibit leaf roll.
Leaf roll does not noticeably reduce plant growth or yield. Some varieties exhibit leaf roll more easily than others. Leaf roll is very common in tomatoes grown in hoop houses.
Another cause of curling tomato leaves is herbicide injury. Tomatoes are very sensitive to injury from broadleaf herbicide chemicals. These are commonly used for controlling weeds like dandelions, plantain and clover in home lawns.
The most common injury symptoms are caused by phenoxy herbicides such as 2,4-D (2,4-dichlorophenoxyacetic acid) and dicamba (substituted benzoic acid). These chemicals are growth regulator, hormone-type weed control chemicals.
Tomato plants usually come in contact with the chemical through spray drift or the use of a sprayer that was previously used to apply the herbicide. It is also possible to expose tomato plants to broadleaf herbicides by using grass clippings from lawns recently treated for these weeds as mulch in the vegetable garden.
Be sure to follow all herbicide label directions regarding the use of treated grass clippings for mulches in vegetable gardens. While there is usually little threat of injury once the lawn has been mowed four to six times after the herbicide was applied, if you are still concerned, leave the clippings on the lawn where they can decompose and provide some nutrients and organic matter back to the lawn.
Contaminated plants show one or more of the following symptoms depending on the degree of exposure and age of plant at exposure.
• Older leaves are excessively pointed, down-curved or rolled with prominent light-colored veins.
• Young leaves do not fully expand and are narrow and elongated with parallel veins.
• Stems are split, distorted or brittle.
• Fruits are cat faced or irregularly shaped.
Plants exposed to small amounts of phenoxy herbicides will outgrow the symptoms without seriously reducing yield or fruit quality. However, harvest might be delayed. Plants do not recover from severe damage by herbicides.
For more information about tomatoes, visit: www.extension.umn.edu.
Until next time, Happy Gardening!