8 Causes Of Tomato Leaves Curling And What To Do

Tomatoes are among the most popular backyard garden crops—and with good reason. They 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, how you can avoid the problem, and how to save your plant.

Why Tomato Leaves Curl

Leaves on a tomato plant that roll downward or curl inward indicate there may be a problem with the plant. Several factors can cause tomato leaves to curl, and some are more serious than others. They may curl during the hottest part of the day or because of lack of rain. They’ll also curl when more serious issues arise. 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.

Other causes include pests, herbicides, and disease. Foliage may bend downward, leaves may be discolored, or growth may be stunted. Other plants may also be affected.

How Do You Fix Leaf Curl On Tomato Plants?

If tomato leaves are curling, the plant isn't a lost cause. Here are some reasons for curling tomato leaves and next steps to take to save your crop.

Insufficient Watering

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.

Maintain an even supply of moisture to reduce stress on the plant, and water at the roots with a drip hose instead of overhead watering to avoid spreading disease. A layer of mulch helps keep the plant from losing too much moisture during evaporation.

Too Much Fertilizer

You can manage environmental stress by avoiding excessive fertilization, especially nitrogen. Once the plant has matured, it doesn’t need nitrogen, and fertilizers containing nitrogen used when the plant is producing fruit may cause curling leaves. In this case, give the plant time to return to normal.

Severe Pruning

Pruning tomato plants can be helpful in promoting air flow and fruit production, but removing too many leaves at one time can cause the plant to protect its remaining leaves by curling them in response. If this happens, give the plant a few weeks to recover and grow more leaves. Prune plants judiciously and hand weed around the base of plants to avoid damaging roots during cultivation.

Excessive Heat

When temperatures sit at a steady high, tomato plants get stressed. Shading plants from the hot afternoon sun can be an option in areas prone to high heat. Plant tomatoes in an area where they get some afternoon shade. Add mulch around the base to hold in moisture, and make sure the plants are sufficiently watered.

Insects

Heavy feeding by insects such as aphids, whiteflies, and thrips can cause tomato leaves to curl because they suck the sap from the leaves. Check the undersides of leaves for insects. If pests are present, use the garden hose to spray a strong stream of water to wash away as many as you can. If needed, use insecticidal soap to control aphids.

Herbicide Drift

Herbicide drift is another common cause of leaf curling in tomatoes. Drift occurs when an herbicide is sprayed in one location, but the 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 damage 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 on 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 miles per hour and use a low spray pressure to increase droplet size, as larger particles are less likely to move with the wind.

Herbicide Residue

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.

How Do You Treat Tomato Leaf Curl Disease?

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 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.