Issue 9, June 21, 2013
Why in the Heck are my Tomato Leaves Curling?
There can be several causes for tomato leaves to roll or curl. Some of the main causes for these symptoms to occur are physiological issues, herbicide exposure, viral infection, or less common problems such as nutritional issues, insect infestation, or phytoplasma infection. When determining the cause of tomato leaf curling/rolling, first take note of any abnormal growing conditions early or during the growing season. Check to see which leaves (old, new, or all) are rolling, determine the direction of the leaf rolling, and whether any other plant parts, including fruit, are showing abnormal symptoms. Therefore, if symptoms are not determined to be a result of virus or herbicide, the cause could be physiological. It takes a bit of detective work to determine the problem and don’t forget there could be a combination of issues.
Physiological leaf roll
Physiological leaf roll can occur at any time during the growing season and is thought to be a growth response to environmental conditions. It is often seen as spring weather turns to summer. The mild spring weather at planting can cause vigorous top growth, even with inadequate root growth. In Illinois, we have seen this condition occur on tomatoes that have experienced unusually hot and dry conditions. Symptoms of physiological leaf roll are usually seen first on the lower, older leaves and have an upward curling of the leaves, which is followed by an inward, rolling of the leaves towards the mid-vein. In addition, leaves can be leathery and thickened, but remain normal in color and size. Not all leaves may show symptoms and leaf veins are not discolored. If environmental conditions and cultural factors are corrected and stress is reduced, the plant can recover; however if this does not occur, all leaves on the tomato plant can be affected. Thus far, physiological leaf roll is not known to affect yield and fruit quality. Some tomato cultivars, usually indeterminate (vine tomato) or those that are considered high yielding, tend to be more prone to physiological leaf roll. Many researchers have reported different causes for physiological leaf roll such as: transplant shock, heat, drought, excessive water, root injury, plants severely pruned or pruned during dry soil conditions, high nitrogen, or phosphate deficiency. No matter the cause, symptoms generally remain the same. Managing this problem can be done by following basic cultural methods such as properly hardening off tomato seedlings before planting, planting different cultivars, maintaining a consistent moisture level in the soil, maintaining temperatures below 95 degrees by shading or evaporative cooling, and avoiding over-fertilization, excess pruning, and root damage.
Tomato suspected to be affected by physiological leaf roll. Picture provided by Andrew Holsinger.
Damage to tomato plants can occur when tomatoes are exposed to chemicals such as herbicides, insecticides, or fungicides. The improper use of pesticides can lead to injury, so be sure to read label directions. Tomatoes are especially sensitive to herbicides such as 2,4-D, a common growth regulator herbicide. Standard symptoms of injury due to various herbicides can include the following: the downward rolling or twisting of leaves, stems that are split, thickened, callused, or twisted, entire plants that are yellowed or chlorotic, and malformed fruits. The level of herbicide exposure will determine survival, but if a plant does survive, the plant should “grow out” of the symptoms, but yield could suffer. The resulting fruit, from chemical injured tomato plants, may not be safe to consume. Some ways to avoid chemical exposure or injury would be to: follow label instructions, avoid applications during high wind speeds, protect sensitive crops, increase droplet size (reduce spray pressure to, use correct nozzles or tips, used drift reducing additives if possible), reduce sprayer speed, and avoid tank contaminations by washing out spray tanks before and between application. Lastly, be sure that the manure, mulch, or compost added to your garden has not been exposed to chemicals that could damage your tomatoes.
Tomato suspected to be affected by an unknown herbicide.
Several different viruses can infect tomato, and these small, infectious, plant pathogens can replicate only inside living cells after they are vectored mostly by humans or insects. Tomato viruses are not considered to be a common problem, and some are known to cause curling of tomato leaves. Depending on the virus, symptoms can also include: yellowing, mottling, mosaic, stunted growth, small leaflets, thickening of leaves, leaf roll, halted growth, purple veins on the underside of leaves, internal browning of fruit, or fruit decline. Tobacco Mosaic Virus (TMV) has been diagnosed at the U of I Plant Clinic. It affects more than 150 herbaceous plants, including tomato, and is usually spread by human activity. It will damage leaves, flowers, and fruits, but does not usually kill the plant outright. A mosaic of discoloration and russetting will appear on the leaves. Plants will be overall stunted, leading to reduced harvest quality and yields. There is no treatment for viruses and it is strongly suggested that plants are removed and destroyed. Depending on the virus, management may also include controlling weeds or disinfecting garden tools.
Tomato found to be infected with Tomato Mosaic Virus (TMV) at the U of I Plant Clinic.
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