What is causing my tomato leaves to twist or curl? There are a number of things that may cause twisting and curling of the leaves and stems. Wind damage, herbicide drift, herbicide residue, broad mites or viruses may all cause twisting or curling.
Wind damage during low-humidity may dry the edges of the tomato leaves, making them twist or curl. This is a self-defense response to prevent further water loss to the plant. Mild leaf roll generally does not lower yields or quality, but severe symptoms may cause flowers to drop and fewer plants to set fruit.
Herbicide drift happens more than people realize. Crops treated in nearby fields for broadleaf weeds may drift off target if not applied at the correct time or correct wind velocity. A wind speed of 5 miles per hour may be enough to drift the herbicide up to a mile. Higher wind speeds may move herbicide miles away, even 8 to 10 miles off the target site.
Tomatoes are extremely sensitive to herbicides. They can be damaged with as little as 0.1 parts per million of the herbicide concentration. If a little of the herbicide comes in contact with the tomato plant, they may recover, but yields may definitely suffer. This would vary for each herbicide used.
Always read and follow all label directions when applying any herbicide. The label will usually indicate if special precautions are needed when using the herbicides. The label may also provide information on wind speed and application of these products under certain conditions.
Herbicide residue may also cause issues to the tomato crop. Even though the product was used correctly and with the label directions, residue may be an issue for some crops. For example, various herbicides for weed control may be used in hay production, and the hay may be used as straw or mulch around the tomato plants. The residue may be strong enough in the hay material that it causes issues to the tomato crop. It is important to know the source of your hay if you use it in the garden to avoid injury to your crops.
Broad mites may affect a number of vegetable crops, tomatoes being one. Broad mites are tiny. They are typically on the underside of the leaves, feeding on the young leaves and flowers. As the mites feed, they inject toxins that severely twist and distort the leaves. These mites are invisible to the human eye and most cannot see them under a magnifying glass. They are detected using a microscope. These mites are 0.10 to 0.30 millimeters long, have oval bodies and can be translucent to pale brown to yellow in color.
Tomato viruses may also cause twisting and curling of tomato leaves. Virus symptoms, look like a number of the other mentioned issues. In Texas, the most common tomato virus is yellow leaf curl virus. New varieties of tomatoes have been developed to resist this virus. If you suspect this or other viruses on your tomatoes, send samples to the Texas Plant Disease Diagnostic Laboratory for diagnosis. This may aid in identification and what to do next. Sample forms and information on the laboratory may be found at http://plantclinic.tamu.edu.
The key to identifying the problem with twisted or curled leaves on tomato plants is identifying the source or sources of the problem. Wind damage may resolve once conditions improve. Mites and viruses may be identified through laboratory or further investigation. Herbicide drift or residue is the most difficult to identify. Regardless of the cause, curled or twisted leaves on tomatoes or other vegetables are a sign that you may need to take action to save your crop.