Tomato Leaf Curl

Have you ever seen the leaves of your tomato plants begin to curl or roll up? Several factors including environmental stresses, viral infection and herbicide damage can cause this odd looking condition, which while it may not mean the complete demise of the plant, can severely stunt growth. Examine the plant to determine the cause of the curling or rolling of the leaves…is it just new leaves or all of the leaves? Do the leaves roll upward or downward? Are any other parts of the plant, including fruit, showing signs of curling?

Physiological Leaf Roll
Over fertilization, and excessive heat, drought, careless pruning, and transplant shock are several of the environmental factors that can cause physiological leaf roll in nightshade varieties like tomatoes. Usually symptoms first appear n the lower leaves with an upward curling of leaflets followed by an inward lengthwise rolling of these small leaves toward the middle vein. The affected leaves often become thickened and have a leathery texture, but may retain normal, healthy green color.

Vine tomato (indeterminate) varieties seem to exhibit physiological leaf curl more frequently than bush tomato (determinate) varieties, and while this condition can occur at any time of the growing season, it usually occurs during the transition from spring to summer. While it is an odd looking condition, tomato leaf curl has little to no impact on plant growth and tomato fruit production. Fully hardening off tomato seedlings before planting, taking care to avoid over fertilizing, and maintaining consistent moisture level in the soil, will greatly help prevent tomato plants from developing this physiological problem.

Viral Infections
Several viral infections may also cause leaf curling in tomatoes. Yellow leaf curl virus, for example is transmitted by whiteflies, and new leaves on infected plants become cupped and pale green in color. The entire plant may also show signs of stunted growth, decline in fruit production, yellowed leaf edges, and purple colored veins on the undersides of leaves. Tomato mosaic virus is another disease that causes curling of leaves, as well as other symptoms, including mottle colored leaves, and internal browning of infected fruit.

There is no treatment for virus-infected plants. It is best to remove and destroy infected plants, and because weeds often serve as hosts to the viruses, managing weeds around your garden can help prevent transmission of the virus by insects. It is also important to disinfect tools that may have come into contact with diseased plants in order to help prevent spreading the virus.

Herbicide Damage: Symptoms of tomato plants that have been exposed to herbicide include downward curling of leaves, twisted growth, deformed fruit, and  stems that split or have turned white. Ultimately the plant’s survival will depend on the level of exposure, and while damage cannot be reversed, new growth on the plant may be normal. Be cautious when spraying herbicide as the mist can drift beyond the target area.