Why Are My Tomato Leaves Curling? Here Are 3 Common Causes

Pests, herbicides, or environmental factors can all cause tomato leaves to curl. Learning to recognize the cause is the first step toward solving this common problem.

Curling Tomato Leaves
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Tomatoes are among the most popular backyard garden crops—and with good reason. Tomatoes are easy to grow, produce high yields, and the home-grown fruits taste far superior to their store-bought counterparts. But growing tomatoes is not without its challenges. One problem growers commonly encounter is twisted or curling tomato leaves. This is caused by a variety of factors, some more serious than others. Learn what causes curling tomato leaves and how you can avoid the problem.

Environmental Causes of Curling Tomato Leaves

Curling tomato leaves are certainly alarming, but sometimes the cause is rather simple. Environmental stress is the most common cause of leaf curling in tomatoes, commonly referred to as rolling or physiological leaf curl. The symptoms of physiological leaf curl vary slightly from other causes. Affected leaves tend to curl upwards and inwards, with damage generally beginning on the lower, older leaves. Environmental stressors can include insufficient water, high temperatures, excessive moisture and/or nitrogen, severe pruning, or root damage.

Tomatoes require constant moisture rather than fluctuating periods of wet and dry soil. Leaf curl symptoms are common early in the growing season when weather patterns shift from wet and rainy to hot and dry. During this transition, plants tend to experience water stress, as the rate of water leaving the leaves exceeds uptake by the roots. Plants respond by curling their leaves to reduce sun exposure, which reduces water loss.

You can manage environmental stress by maintaining an even supply of moisture and avoiding excessive fertilization, especially nitrogen. Prune plants judiciously and hand weed around the base of plants to avoid damaging roots during cultivation. Shading plants from hot afternoon sun can be an option in areas prone to high heat.

Herbicide Damage can Cause Tomato Leaves to Curl

Herbicide drift is another common cause of leaf curling in tomatoes. Drift occurs when an herbicide is sprayed in one location, but wind carries the herbicide to another location. Wind speeds as low as 5 mph can cause drift and unfortunately, tomatoes are very sensitive to herbicides. The damage caused by herbicide drift looks different from environmental stress. Typically, herbicide damaged affects the new growth first. Symptoms may vary according to the specific herbicide in use, however affected foliage tends to bend downward with leaflets cupping or curling. Herbicide damage also tends to affect many plants in the garden, not just tomatoes.

Herbicide damage can occur from chemicals sprayed on your property or a neighboring property, with commercial agriculture fields being a common source for gardeners in rural areas. You can minimize herbicide damage by minimizing herbicide use in the landscape, following label instructions carefully, and using a hooded sprayer when applying herbicides. Avoid spraying when wind speeds exceed 5 mph and use a low spray pressure to increase droplet size, as larger particles are less likely to move with the wind.

Another source of herbicide damage is residue in mulch or compost made from hay or manure that has been treated with aminopyralid. Residue from this herbicide can persist on treated hay and hay products for 18 months. It also passes through the digestive system of grazing animals, remaining in the manure of animals that ate treated hay. This source of damage is easily avoided by purchasing manure and hay from a reputable source and asking if the source material was treated with aminopyralid.

Viral Infection Can Cause Curling Tomato Leaves

Tomatoes are susceptible to many viruses, such as tomato yellow leaf curl virus, that cause leaves to twist and curl. Initial symptoms resemble herbicide damage, commonly affecting newer younger foliage, but viral diseases tend to progress and additional symptoms aid in identifying infection. Symptoms such as stunting, discolored foliage, leaf vein discoloration, and irregular growth commonly occur along with leaf curling.

There are no chemical controls for viruses and affected plants do not recover, they will die or remain stunted without setting additional fruit. Remove infected plants as soon as possible to reduce further spread. Plant viruses are transmitted by insects or on dirty tools. To minimize infection, always clean and sterilize pruning equipment between plants. Manage insect vectors by reducing weeds in and around the garden and treating pests when outbreaks occur. The most effective measure you can take in limiting viral infection is planting disease-resistant varieties. Look for resistant varieties when selecting tomato plants for the garden.

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