Tomato Leaf Roll
Posted: July 17, 2012
A: This is called leaf roll. Usually seen on older leaves, the leaflets curl up lengthwise, sometimes into a very tight roll, and they often become thick and leathery as well. Although you may find an insect or spider hiding in that rolled up leaflet, the critter is not the cause of the problem, nor is this a disease. It is a physiological condition, a functional response of the plant to some stress factor, and it is worse in some tomato varieties than in others.
The recent very hot and dry weather is most likely the stressor in this case. The plant senses it is losing more moisture through the leaves than can be replaced through the roots, so it tries to compensate by rolling the leaves and making them thicker to reduce water loss.
Other stresses that can lead to leaf roll include heavy pruning, excessive fertilizer, cultivating too close to the roots, saturated soil, or any sudden change in weather. It often happens when mild, rainy spring weather transitions to hot, dry summer weather, and the plant’s top growth has outstripped root formation.
Fortunately, leaf roll is not something you need to worry about, as it does not affect growth or yield, and will often correct itself when conditions become more favorable. To minimize leaf roll on tomatoes, use mulch to keep the soil at more even temperature and moisture levels; don’t damage the roots by cultivating or hoeing too close to the plants; and water well to keep the soil moist, but don’t overwater so it stays saturated – soil needs to dry out slightly between waterings.