Answer: The rolling or curling of tomato leaves can be a symptom of environmental stress, herbicide damage or viral infection.
Physiological leaf roll may be associated with environmental stresses such as excess moisture, excess nitrogen, and transplant shock. Leaf roll may also be related to moisture conservation during periods of extreme heat and drought. Improper cultural practices such as severe pruning and root damage during cultivation can also cause leaf roll symptoms. Physiological leaf roll involves an initial upward cupping of the leaves, followed by an inward roll. In severe cases, the leaves roll up until the leaflets overlap. Symptomatic leaves become thickened and leathery. Symptoms typically appear first in lower leaves but may spread to the entire plant, depending on the severity of the condition. Leaf roll is more commonly associated with staking varieties of tomato, such as "Early Girl" and "Big Boy", rather than bush types. In most cases, the condition is temporary and will have little or no affect on plant growth or fruit production.
Tomato leaf roll symptoms may also be a direct result of herbicide injury. 2,4-D is a hormonal herbicide commonly used on lawns to control broadleaf weeds such as dandelion and chickweed. Tomato plants that have been exposed to 2,4-D drift exhibit downward curling of the leaves and overall deformed, twisted growth. Leaf veins are light coloured and very prominent.
Curly Top is a viral disease carried by leaf hoppers. Leaves of infected plants are dwarfed, crinkled, rolled inward, and cupped upward. Veins on the underside of leaves usually have a purple discoloration, may be roughened, and often produce swellings or spine-like outgrowths. Affected plants do not recover and die or remain stunted without setting additional fruit.
Tomatoes infected with the cucumber mosaic virus develop a slight yellowing and mottling of the older leaves. Expanding leaves typically become twisted, curl downward, and develop a "shoestring" appearance as a result of a restriction of the leaf surface to a narrow band around the midrib of the leaf. Diseased plants are stunted and produce small quantities of fruit.
If your plants have one of these viral infections, there's no way to save them so I hope the problem is due to environmental stress!
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