Troubleshooting Tomato Plant Leaves Curling

Written by: MIgardener Team

Published on May 29, 2022

Updated on November 15, 2024

Tomatoes are an heirloom gardener’s best friend. So when gardeners see their tomato leaves curl, they often jump to the worst-case scenarios like herbicide damage or curly top virus. But the cause of tomato plant leaves curling may not turn out to be so bad after all.

Learn to differentiate the potential causes so you can respond correctly to the issue. Let's make your tomato plants healthy and happy again!

Are Your Tomato Plant Leaves Curling

When it comes to growing tomatoes, the thing I love most is how many heirloom varieties exist. You could try a new variety every year and you would be about 4,000 years old before you’ve tried every single variety.

You can find seeds to grow some of these great heirloom varieties right here on the MIgardener website: from the super productive Ace55 slicing tomato to the delicious Red Pear cherry tomato, the little-known Federle paste tomato, and the versatile Red Centiflor tomato that will absolutely blow your mind.

But there is also a world of pests, diseases and deficiencies to deal with when growing tomatoes, such as tomato blight, tomato hornworms, powdery mildew, and curly top virus.

While those are all very specific problems, a handful of tomato issues can also be identified simply by examining why your tomato plant leaves are curling.

What Is Tomato Leaf Curl

Tomato leaf problems are the most frequent tomato problem in the garden, especially if you are growing non-heirloom varieties. You can tell a plant has tomato leaf curl if the leaves twist, roll, or curl.

While leaf curl may not kill your plant, it is ultimately never a good thing to have as it’s an indicator that something is wrong, and it’s time to investigate.

What Causes Leaf Curl

Tomato leaves can curl for a wide variety of reasons, but the 3 main causes are:

Cause	Potential Source	Impact on Plants
Herbicide Damage	Herbicides, such as Grazon, can enter the garden through straw or hay bales used as mulch. Other herbicides can enter your garden when sprayed nearby and drift in on the wind.	Herbicides can stay in garden soil for years, stunting new growth of plants, causing leaf curl, and inhibiting new leaf development.
Pest Damage	Aphids, whiteflies, and thrips can spread viruses, but the most common pest culprit is the leafhopper. The leafhopper excretes saliva while feeding on the plant, which can become infected with the leaf curl virus. The good news is that the Curly Top Virus does not spread from plant to plant. Only leafhoppers spread this virus.	Infected plants will show stunted growth, leaf yellowing or browning along the edges, reduced leaf size and cupping.
Heat Damage	The plant reacts to extreme heat by curling its leaves, reducing the surface area exposed to the sun.	The leaves are like mini solar panels, so when the plant has a sufficient amount of sunlight, they close to prevent sunburn. Once the extreme heat has passed, the new growth should look normal.
Too Much or Too Little Water	If the plant does not have enough water, it will curl its leaves to reduce sun exposure, as the sun can increase dehydration. With too much water, root rot can occur. Leaves curl when the plant cuts off the water supply to the leaves.	Underwatered plants will look withered, while plants with root rot will exhibit mushy stems, yellowing leaves, and stunted growth.
Strong Winds	High winds can dry out the leaves. Often, the most exposed leaves curl to protect themselves.	When the winds subside, the plant can often recover and continue to grow, thrive, and produce fruit.

Identifying Tomato Leaf Curl

As we have discussed, the cause of curling leaves may be temporary or more permanent and severe. The biggest thing I want to make clear is how to diagnose the likely cause so you know how to treat it.

Identifying Herbicide Damage

To identify herbicide damage, take a look at the garden as a whole. If you have tainted soil, introduced herbicide through mulch or compost, or spray drift, you should see much of your garden being affected, not just select tomato plants.

If herbicide damage is your culprit, look at all the areas you suspect contamination. If contamination has occurred, you should see widespread plant health issues. If you are growing peppers, potatoes, beets, basil, or other plants in the same area, all of these plants will show damage.

Plants grown in soil tainted with herbicides will start out great for a few weeks, but suddenly, the top leaves will get curly, yellow, and stunted. The plant will struggle to form new leaves and grow. Over time, this will cause poor growth and yields, and eventually, the plant will die.

If your issue is not broad but localized, that is great news! You should be able to rule out herbicide contamination.

Identifying Curly Top Virus and Pest Damage

Again, look to see if this is a localized issue. If leafhoppers are causing curly top virus, I would expect to see one plant here and there with curled leaves. Because the curly top virus does not spread from plant to plant, the plants next to the affected one should look healthy.

Also, if a plant has the curly top virus, the leaves will not just roll inward; they will look crinkled and yellow with purple discoloration in the veins.

If you suspect other types of pests, a visual inspection of your plants to find insects or egg deposits is the best way to identify the cause.

Identifying Environmental Damage

If leaf curl was caused by environmental damage, it would be broad across most of your tomato plants that experienced that environmental condition. New leaves and flowers will continue to form normally, and the new plant growth won’t be curled. If new leaves are forming curled, that would indicate herbicide damage, pests, or disease.

Cause of Leaves Curling Up - Leaves that curl up are very common. This type of leaf curl is a response to environmental issues almost 100% of the time. Whether strong winds, insufficient water, or extreme heat, your tomato plant should continue to thrive when the condition is corrected.
Cause of Leaves Curling Down -Root rot occurs when over-watering causes the plant to stop water uptake. The roots of the plant contract and close to prevent the plant from dying and the leaves will curl downward. Eventually, if the plant continues to be overwatered, the roots will rot, and the plant will die.
Cause of Leaf Curling at the Base of Plant - Tomato leaves curling only at the base of the plant is a sign of a micronutrient deficiency. However, you should be able to tell that there is a problem long before any curling occurs by yellowing leaves.

How to Treat Leaf Curl

Now that we have diagnosed what is causing leaf curl on your tomato plants let’s talk about the solutions:

Issue	Treatments and Solutions
Herbicide Contamination	You will need to remediate your soil. Remove all the contaminated soil from your garden and replace it with good soil.
Curly Top Virus	The curly top virus is the end of the plant. It can’t be healed. You will want to pull that plant up and start from scratch with a new plant.
Pest Damage	Consider organic treatments or sprays specific to the pests you find on your plants.
Environmental Factors Like Extreme Heat, Strong Winds, and Sun	This can be healed, and you don’t have to do much. Even though affected leaves won’t uncurl, the plant should continue to form healthy new growth and flowers.
Insufficient Water	If insufficient water is the culprit, increase watering during the dry weather. Most tomato varieties require 1 to 2 inches of water per week under normal conditions. A drip irrigation system is helpful to manage water delivery and prevent evaporation.
Root Rot From Too Much Water	Plant tomatoes in well-draining soil. They don’t like soggy feet, so don't let them sit in water. Water tomatoes once the top inch of soil is dry.
Micronutrient deficiency	There are a few easy fixes to this issue. Add Azomite , which is a clay compound packed with minerals and micronutrients that are often washed away in modern soils. Or try adding fresh compost or an all-purpose fertilizer, like Trifecta+ , as a soil amendment to get your plants back on track.

Following these tips should solve any issues you may have with tomato plant leaves curling, so get out there, garden with confidence, and grow bigger!

FAQ

What is tomato leaf curl?

Tomato leaf curl means the leaves twist, curl, or roll. It can be caused by herbicides, pests, or environmental factors.

Why do my tomato leaves curl upward?

Leaves curl up when it's too hot or dry and the plant gets dehydrated. It's the plant is trying to save water.

What causes the leaves on my tomato plant to curl downward?

Downward curling leaves mean you might be watering too much or have too much rainfall.

What are the symptoms of Curly Top Virus?

Curly Top Virus makes plants grow slow, turn yellow, and curl leaves up. Leafhoppers spread the virus by feeding on plants.

How does herbicide exposure cause leaf curl?

Herbicides can make leaves curl up. They make growth twisted, leaves look wrong, and make them break easily. Know the difference from other problems and use herbicides carefully to prevent it.