This past two weeks I have noticed some of my tomato leaves have been curling up. A couple of visitors to my garden suggested that perhaps I had a virus or something contagious that could infect my other tomatoes. I had to go check it out because I really was not sure what I had. Here is a photo:
After a little research, I have decided I do NOT have a virus (curly top or tomato yellow leaf curl), but the hot weather in Idaho has brought on physiological leaf roll.
The symptoms appear similar to a virus, but it is a physiological condition which does not affect the tomato yield or quality. As you can tell from the photo the leaves roll upward. Apparently, cultivars that are most affected are those that are high yielding tomatoes. The tomatoes in my garden that are most affected are the Prinicipe Borghese, a determinate tomato that gives very high yields. None of the other tomatoes in the garden are as greatly affected. I have noticed that the new growth is just fine and shows no evidence of rolling.
For more information, go to this link: http://cru.cahe.wsu.edu/CEPublications/PNW616/PNW616.pdf
If you don't want to read this study, I will tell you that the leaf roll can be caused when plants are pruned during dry soil conditions or if there is excess soil moisture and prolonged high temperatures. In Idaho, we have had several weeks of high temps, but now that the weather is cooling down, there should be less leaf rolling here. To manage the leaf rolling, the study recommends to keep uniform soil moisture, avoid tomato pruning, don't over fertilize and provide shade or cooling for the plants.
As an Idaho gardener, I rarely prune tomatoes because it can produce sunburn on the fruits.