Many gardeners become concerned when tomato plants exhibit “leaf curl” or “leaf roll”. The leaves begin to turn upward at the edges and roll inward. Fortunately, tomato leaf curl is typically a physiological disorder, not the result of a disease or virus. Also, according to The Pacific Northwest Vegetable Extension Group… “Plant growth, fruit yield, and fruit quality are not believed to be affected by physiological leaf roll”.
Factors affecting Tomato Leaf Curl
The Pacific Northwest Extension identified several factors that may contribute to physiological leaf roll of tomatoes. Here is my summary
of the key causes:
1. Severity is cultivar-dependent, with high-yielding varieties being the most susceptible.
2. Indeterminate cultivars are more susceptible than determinate cultivars.Indeterminate (vine) tomato varieties will continue to grow until killed by frost or disease. The plants can become quite large and often outgrow their cage or trellis. They will continue to produce fruit throughout the growing season.Determinate (bush) tomato varieties have a more compact growth habit. They stop growing when fruit sets at the terminal growth point. Some growers like determinate types because they tend to ripen all tomatoes on the plant around the same time.
3. Symptoms are more common on plants that are pruned during dry soil conditions.
4. High-yielding cultivars grown with high nitrogen fertility.
5. Phosphate deficiency.
6. Extended dry periods.
7. Excess soil moisture coupled with prolonged high air temperatures (above 95 degrees).
The photo above was taken in my garden during the Summer of 2015. That year, we experienced a combination of two factors from the list above: #6 extended drought and #7 excessive heat. I was fairly successful at keeping my tomato plants watered; maybe to excess. But, I believe heat and overall dry conditions were the key factors for leaf roll on those plants.
Symptoms of Physiological Leaf Roll
With physiological leaf roll, the rolled leaves become rough and leathery. But, they don’t have discolored veins and are normal in size and appearance (except for being “rolled up”). If rolled leaves also exhibit yellowing, lesions, or mottling, that may indicate the presence of disease.
If your tomato plants show physiological leaf roll (leaf curl), you may be able to alleviate the symptoms if you can address any of the issues listed above. Since overall growth and fruit quality doesn’t seem to be impacted significantly, I wouldn’t stress over it.
To read the complete article, click Physiological Leaf Roll of Tomato from the Pacific Northwest Extension