Tomato Leaf Curl: What It Is And How To Fix It

One common problem that plagues gardeners is tomato leaf curl. This symptom can be caused by many factors and the key is to correctly identify the issue before administering a solution. 

Tomatoes are one of the most commonly grown plants and take the pride of place in many gardens.  From gorgeous heirlooms to prolific hybrids, there is a tomato plant out there for everyone. Nothing beats the taste of a tomato straight off the vine, but tomatoes can also be a bit tricky to grow.

There are some key factors to look for when identifying the causes of tomato leaf curl. Watch to see if the leaves curl upward or downward, whether they appear to have any insects on them, whether they’re brown or yellow in color, and other unusual factors. These can help you identify what the problem truly is, as you’ll soon learn!

Possible Treatments For Causes Of Tomato Leaf Curl:

What Causes Tomato Leaf Curl?

Tomato leaf curl
An example of a plant experiencing severe leaf curl caused by damage to the plant.

Tomato leaf curl is akin to a stomach ache in humans. Some causes are benign and others are a symptom of more severe problems. Additionally, some can be easily remedied while others are untreatable. 

One of the best practices of gardening is to frequently inspect your garden for any signs of damage and take preventative actions through learned experience. We can classify the causes of leaf curl into several broad factors: environmental, chemical, and biological. We will do a deep dive into each problem in the following sections. 

Environmental Stress

For many gardeners who purchase tomato seedlings in the spring, you may find that your tomato plants will thrive for a few weeks and suddenly develop leaf curl. This is a type of physiological leaf curl or leaf roll that is triggered when the weather suddenly gets too hot and dry and there may be inadequate root development. Physiological leaf roll will start at the bottom of the plant with older and lower leaves and work its way up the stem. Tomato leaves cup inwards and can appear leathery. Affected leaves will still retain their green color. Usually, plants recover from physiological leaf roll and environmental stress with proper cultural practices, so the fruit yield should not be affected. 

An indeterminate tomato plant can grow to be very tall and become susceptible to wind stress and damage. If not properly staked and supported, the plant can become twisted, leaves will curl and tips of these tomato leaves may die back. This damage will look similar to that of herbicide damage, but you should be on the lookout for high wind events in your area and be able to pinpoint this cause.

Gardener Error

Every plant has its own unique environmental needs. It is important to consider the environmental conditions that your tomato plant is best adapted for and try to recreate those conditions in your garden. Tomatoes prefer well-draining soil. When soil is saturated with water and there is excessive moisture around the root system, it removes air pockets and creates conditions for infections and root rot. Root rot will cause tomato leaves to roll, change color from green to brown, and droop. Use a moisture meter or just your fingers to check how soggy the soil is and let the soil drain fully before the next watering. 

Pruning can also stress the tomato plant. Although gardeners are taught to pinch suckers from tomato plants, you must remember that leaves are how plants make food and convert sunlight into energy. Over-pruning a young or poorly established plant can cause enough stress to stunt plant growth and decrease fruit production.

Herbicide Damage

Herbicide damage on tomato
Herbicide damage on tomato leaves.

Tomatoes are sensitive to chemical drift, in particular to the herbicide 2,D-4. Chemical drift happens when agricultural or weed control sprays are carried by wind and deposited away from the intended area. In contrast to physiological leaf curl, plants that experience herbicide damage may have leaves that curl downwards, look twisted and have malformed fruits that are not safe for consumption. Other symptoms may include yellowing leaves or split stems.

Keep a close eye on the new leaves of these plants. The tomato may be able to recover from herbicides and still yield a good crop. If you notice curling leaves on new growth, you may want to pull out the plant entirely and start again. Make sure the manure or compost that you use in the garden has not been contaminated. Herbicide damage can persist for a few years in your garden if the chemicals are left in the soil and continue to be a problem for future plants.

Insects

Aphids are a large family of pests with over 4,000 species and is a common issue for tomato plants. They attack plants by removing sap from leaves and stems with their mouthparts. If left unmanaged, aphids may stunt plant growth and lead to a smaller fruit yield. Damage leaves may be curled, puckered and with pale yellow spots. Aphids are commonly found on the underside of leaves and can be seen with the naked eye. Look out for their tiny bodies and dew droplets that they secrete. 

Broad mites are another group of pests that can be found on the underside of leaves. They attack a wide range of plants including peppers and tomatoes. Broad mites prefer tender young leaves and will start feeding from growing tips and flower buds. The new growth will turn brown and curl up. Like with aphids, broad mites are visible and can be easily identified on leaves where there is damage. Broad mites also spin webs on the underside of leaves so that is a sign to look out for. 

Diseases

Tobacco mosaic virus in tomato
Tobacco mosaic virus damage to a tomato plant.

A less common cause of leaves curling can be due to viral infections. The tomato mosaic virus (ToMV) and tobacco mosaic virus (TMV) are both diseases that can impact tomato plants and they have very similar symptoms. Young tomato plants may have stunted growth with small leaves curling upwards. Both viruses are spread predominantly through human activity such as from the gardener’s hands from one plant to another. There are many disease resistant varieties of tomatoes that are bred to handle these viral strains. For example, “Health Kick” and “Sophya” are disease-resistant varieties of hybrid tomatoes. 

The Tomato Yellow Leaf Curl Virus (TYLCV) was first identified in a greenhouse in California in 2007. Although yellow leaf curl virus was found in other parts of the world, it was not introduced to the Americas until the 1990s and has since had a severe outbreak in Mexico that devastated fruit production during the 2005-2006 growing season. This is a damaging virus that stunts the growth of the plant and limits its fruit yield. The yellow leaf curl virus is spread by sweet potato whiteflies and can impact a range of host plants. These whiteflies cannot tolerate cold winter temperatures so should not be an issue for many growing zones in the U.S. and Canada. The telltale symptom of this viral infection is short bushy plants with small leaves curling upwards and the yellowing of leaves along the veins. 

Remedies For Tomato Leaf Curl

Cultural Practices

Environmental causes of leaf curling are the most common and usually treatable. Essentially, you can view leaf curling as a way the plant is communicating something is wrong. Check the growing conditions around the plant. Use your fingers to gauge the soil moisture level and observe, throughout the day, how much direct sun your plants are getting and how hot the temperature is outside. These plants need good drainage and consistent watering. Consider using a soaker hose on a hose timer, or hand water deeply rather than sprinkling water from the top of the plant. Tomato plants are susceptible to fungal infections and it is important for the leaves to stay as dry as possible. Generously apply mulch around the plant to help maintain soil moisture. 

Although tomatoes thrive during the summer, they can still be stressed by high temperatures, high dew points, and heavy rains. Tomato plants can also get sunburnt! Depending on the cultivar, tomato plants can start to experience sunburn when the temperature rises above 100 F. Using a 30% sunblock shade cloth is a good way to protect your plants and these shade cloths can be reused year after year. 

Secure the shade cloth onto your tomato stakes and spray them with a preventative fungicide. The cloth can stay over the plants for the entire growing season, depending on how many days you may have over 100 F degrees. Pests target stressed plants so keeping your plant healthy is a natural way to prevent pests like aphids and mites. 

Tomatoes are hardy, fast-growing vining plants. During planting, anticipate indeterminate varieties to get very large and will need a structure to support their growth. Regardless of the method you use, whether it is using stakes, cages, or trellises, securing your plant to the support structure can prevent or limit wind damage. Prune excessive suckers and lower leaves to allow more airflow. Also, prune leaves that have visible aphid or broad mite infestation as one step in their population control. 

In addition to pruning, plants that are infested with aphids or broad mites can be treated by using a forceful stream of water to wash off the pests. Make sure to spray the water early in the morning to give the leaves ample time to dry off as the weather warms. If necessary, neem oil or insecticidal soap can be used for moderate infestations, or pyrethrins for really severe ones.

When Treatment Fails

Sometimes it is just not possible to save a tomato plant no matter how much we try. That’s why it’s important to always have a few plants ready to go in case the current ones in your garden fail. As you prune tomato leaves, you can easily root suckers in water as backups. If the weather is not cooperative and the plant just does not make it, you can compost the plant.

However, you need to be attentive to the main causes of death before composting. If you have an infected plant due to a leaf curl virus or have a plant that suffers from herbicide damage, it’s important not to compost your plant because the virus or chemicals can linger in the soil and be passed on to future plants.

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