David Cantrell

The most asked question of the week, why are the leaves curling on my tomato plant?

Tomato leaf curl can be caused by a variety of things, in this article we will focus on the most common things that usually cause the problem.

Leaf Roll, or leaf curl is a physiologic distortion that may develop with periods of cool rainy weather. It causes the lower leaves to roll upward and become thick and leathery. Tomato leaves curl naturally if it’s too hot, too humid or too windy. In other words, the leaves will tend to curl if growing conditions are not optimum for the plant. If it’s too hot and dry, water more deeply. If it’s too wet water less frequently (make sure you water deeply though).

Another possible cause is herbicide damage, particularly from 2,4-D. Herbicide damage causes leaves to curl first downwards and then upwards. Fruit may also show a condition called “cat face”. The general appearance of the plant is stunted growth and twisted leaves. If the exposure is mild or minimal, such effects aren’t seen and any damage will be outgrown. If the exposure is extreme the plant will often die.

Viruses may cause a tomato leaf to cup first downwards and then up. Virus such as Beet Curly Top and Tomato Yellow Leaf Curl both cause leafs to curl. Both are transmitted to the plant by insects with sucking mouth parts (beet leafhopper and sweet potato whitefly). Long term damage to the plant depends upon when during the tomato’s plant growth the virus is transmitted. In the case of Beet Curly Top affected plants do not recover and die or remain stunted without setting additional fruit.

One additional cause of leaf curl could be the excessive use of nitrogen fertilizer. Too much nitrogen can burn the root system and cause the leaves to curl. The affected leaves will remain curled the entire life of the plant and reduction in fruit will also been seen. If the roots are burnt bad enough the plant will often be stunted or die.

For more information on garden management contact your local OSU Extension Office