Leaf roll is a problem which affects many plants and vines including grapes, tomatoes, eggplants, and potatoes. There are a number of different causes for leaf roll; depending on the cause, the condition can be harmless, or very serious. Most home gardeners deal with environmental leaf roll, which is easy to address with changes in gardening techniques. Some people struggle with herbicidal leaf roll, which is caused by exposure to herbicides, while vineyards in particular have problems with viral leaf roll, a highly infectious type of leaf roll which is passed along a variety of insect vectors.
In the case of environmental leaf roll, the problem is caused by infrequent or erratic watering, and sometimes by dramatic weather changes as well. Plants start to coil up their leaves to reduce leaf surface area in an attempt to promote root growth to make the plants stable and healthier. Environmentally caused leaf roll is not harmful, although it looks unsightly; it can be prevented with regular deep watering which keeps plants moist without waterlogging, pruning lightly, and by working carefully, if at all, around the roots of plants with tools like hoes and spades.
In the case of herbicidal leaf roll, the plant responds to an herbicide in its environment. People who use herbicides to control undesirable weeds face the risk of leaf roll, which is also accompanied with a twisted, gnarled growth habit. If caught early, this type of leaf roll is recoverable, but in other cases it can permanently damage affected plants, or cause them to produce very misshapen and unattractive fruit.
Viral leaf roll is transmitted by insects. The veins on the underside of the leaves may turn purplish, which distinguishes the viral form of this plant disease from other forms. Leaves will start to turn spotted and they will become malformed and lumpy, while fruit may be severely deformed, if it appears at all. Plants affected with viral leaf roll should be torn out and destroyed before the disease spreads to the rest of the crop.
If you notice signs of leaf roll in your garden, check the leaves for the characteristic purple veins which indicate viral infection. If veins are not present, you may want to reform your watering and weeding practices, or cease the use of herbicides, if you use them. Gardeners who continue to struggle with leaf roll may want to check with their neighbors to see if the neighbors use herbicides or if they have been having a leaf roll problem as well, which might indicate viral infection.