Tomato Leaves Curling? These 4 Common Causes Could Spell Serious Trouble for Your Plants

Tomatoes are one of the most popular garden crops, but they aren’t without their problems, like tomato leaves curling. Just about every tomato grower sees this issue at one time or another, but it is always an unwelcome sight.

Tomato leaves curl up in an effort to protect the plant from a variety of causes. Most are not life-threatening to your tomato crop. But determining the cause of this common tomato plant problem and treating it is essential to growing strong, healthy plants that produce lots of fruit.

Curled tomato leaves may stem from an environmental change, herbicide drift, insects, or viruses. I’ll walk you through how to determine the exact cause and how to treat each one so you can still grow a huge harvest of tomatoes.

What Is Tomato Leaf Curl?

Tomato leaf curl is just what it sounds like. You may see your tomato leaves curling or rolling up and beginning to appear crumpled. Plant growth soon becomes stunted. Tomato flowers may not develop or those that do simply fall off. As a result, tomato production may also be significantly reduced.

Leaf curl can start out slowly, but speed up as new growth appears. Sometimes all the leaves are affected and sometimes only new growth is curled. Your tomato leaves may turn yellow or twisted as well.

Why Are My Tomato Leaves Curling?

There are several possible causes of tomato plant leaves curling or rolling up. It can happen at any time during the growing season. Curling leaves occur more frequently on indeterminate tomatoes rather than determinant plants. Heirloom tomatoes also have this problem more often than hybrid cultivars.

The first step in treating this issue is pinning down the source of your plant’s affliction. A number of factors can cause curling tomato leaves, some more serious than others. The issue may be environmental, chemical, biological, or even a combination.

Here are the main culprits and how to determine which one is affecting your plants:

1. Environmental Factors

Environmental factors such as drought, overwatering, high temperatures, wind, or too much nitrogen can result in physiological leaf roll. Other causes include premature planting, transplant shock, or a lack of phosphorus.

Curling leaves also occur when spring temperatures move into summer highs. When a plant is hot and unable to take up enough water for the foliage to use, leaves start to roll inward lengthwise. This usually begins in the lower, older leaves first.

It is a self-preservation move that reduces the amount of surface area exposed to the elements. Often the affected leaves thicken and develop a leathery texture, even while retaining their normal green coloration. Plum and paste tomato varieties are most commonly affected by this cause.

On the other hand, cool and moist conditions can make leaves roll upward and become leathery in an effort to repel excessive moisture. This specific condition occurs around fruit setting time and is most commonly seen on staked and pruned plants. It affects indeterminate tomatoes more than determinate tomatoes.

It is important not to overfertilize tomato plants either, not only to prevent leaf roll and fertilizer burn, but because too much nitrogen can promote leafy growth at the expense of fruit set. Leaves also may curl in response to heavy pruning or root damage, too.

2. Insects

Damage from sucking insects such as aphids or whiteflies can cause leaf roll or twisted leaves. Check the undersides of the leaves for these invaders. Neem oil or insecticidal soap should take care of them, if a blast of water is not enough.

Another pest, broad mites (Polyphagotarsonemus latus), injects toxins into leaves and flowers while the mites are feeding. These almost microscopic insects attack a variety of veggies and flowers, targeting the young and tender foliage first. The result is twisted and deformed leaves.

The mites are not visible with the human eye, but you can detect their presence by examining the undersides of leaves, which will show a bronzing effect. You may be able to see their eggs, which are white and oval-shaped with ridges. Your closest extension office can confirm the presence of broad mites on leaf samples.

Severe infestations require removal of the plant. Moderate problems may be treated with neem oil or insecticidal soap, both of which you can find on Amazon.

3. Herbicide Drift

Herbicide damage happens when you or your neighbor sprays herbicides and some of the chemicals drift into your vegetable or ornamental garden. It can happen when there is a breeze or if the plants are close together.

Chemicals can drift as far as one mile, so be wary if fields are being spayed nearby. Common products that cause herbicide and pesticide drift in tomatoes include 2, 4-D, dicamba, or contaminated compost that contains herbicides.

Tomatoes are highly sensitive to herbicides. Symptoms vary somewhat depending upon the herbicide, but generally leaves roll downward and foliage and stems become twisted, especially in new growth.

The leaves may curl up tightly, making a “C” shape. The plant may become stunted or deformed. Adventitious roots may also appear along the stem like small bumps or stems may turn white and split. Flowers and fruit may also be affected.

There is no remedy for herbicide damage and the plants should be removed.

4. Viruses

Curling tomato leaves may be a sign of several viral tomato diseases. Normally viruses are transmitted through pests or infected transplants. There are a few different viruses that can cause curling leaves on tomato plants.

Viruses such as tomato mosaic virus (TMV) or beet curly top virus (BCTV) can show symptoms similar to herbicide drift or physiological leaf roll. However, with TMV, the plants also display mottled mosaic leaf patterns and the infected fruit is brown inside. When affected by BCTV, the leaves may roll upwards and turn a yellowish color with purple veins.

Cupped, pale green leaves may indicate a tomato plant is infected with tomato yellow leaf curl virus (TYLCV). It is part of a group of “geminiviruses” that can spread to tomato plants via the sweet potato or silver leaf whitefly.

Tomato yellow leaf curl virus is one of the most common, but other viruses such as chino del tomato virus, tomato leaf crumple virus, and tomato yellow streak virus are all caused by whiteflies.

Your local extension office may be able to positively identify which one is impacting your plants as well as other viruses through a diagnostic lab. However, there is no cure for tomato viruses.

The best way to prevent their spread is to pull up and discard the affected plants in the trash. Do not compost them or you risk spreading the virus to other plants in your garden.

How to Treat Tomato Leaf Curl

While the damage may look similar regardless of the cause, the methods of control are very different. To help prevent tomato leaf rolling and twisting, follow these suggestions below for each different cause.

For Environmental Factors: In the case of environmental factors, prune tomatoes conservatively, avoid excess fertilizer (especially those high in nitrogen), be consistent with irrigation, mulch around tomato plants to help retain moisture, and shade plants from high heat whenever possible.

For Pests: Stay vigilant for common tomato pests and act quickly when you spot them. It also helps to protect garden plants from possible whitefly infestations by adding floating row covers, which you can get on Amazon.

For Herbicide Drift: Avoid spraying herbicides on windy days. It also helps to shield nearby plants with large pieces of cardboard. Areas that have been poisoned by herbicide drift should lay fallow for a season or two. Or you can grow a cover crop in that area.

You may also want to rotate to a crop that’s more resistant to herbicides, such as turnips or kale. The herbicide will eventually break down – you just have to wait it out.

For Viruses: Although tomato leaf curl may not affect the overall growth or yields, when the problem is caused by a viral infection, it may be necessary to entirely remove the infected plants.

Start by selecting disease-resistant tomatoes at the beginning of the season to prevent this issue. Botanical Interests has a lot of great disease-resistant tomato seeds to choose from.

Also, consider choosing determinate plants, which are less prone to leaf curl. Weeds can act as hosts to viruses, too. So be sure to control weeds around your tomato crops, taking care not to damage plants’ root systems.

It is also helpful to sanitize tools used on diseased plants. You may want to destroy tomato plant leaf curl infected plants to prevent any further transmission to those nearby.

If the leaf roll is not severe, quality and quantity of the fruit is usually unaffected. However, severe leaf roll that affects the entire plant may result in flower drop and fruit loss.

Looking for additional tips on growing perfect tomatoes? Download our FREE Tomato Growing Guide and learn how to grow delicious tomatoes.