Tomato Leaves Curling: 10 Causes And How To Fix Them

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Tomato plant leaf curl is a common problem that many gardeners experience. Leaf curling can be caused by a variety of factors, such as environmental stress, viral diseases, herbicides, and insect infestation.

In this article, we will be discussing the causes and what you can do to prevent or remedy the issue.

Table of Contents

Types Of Tomato Leaf Curl

First, let’s go over the different types of tomato leaf curl so that you can properly identify the issue.

Leaves Curling Or Rolling Up

If a tomato plant is exposed to too much sun, heat, or wind, or if there’s a lack of water, the leaves will curl up as a form of protection.

This response is the plant’s way of retaining moisture and reducing the amount of surface exposed to harsh elements. The curling may extend to the leaves on the upper parts of the plant or just the leaves near the bottom.

When the environmental issue has been resolved the leaves will go back to their normal state.

Leaves Curling Or Bending  Down

If you notice that your tomato leaves (not separate leaflets, but sets of leaves) are curling downwards, this could be a result of root rot caused by overwatering, which results in a lack of nutrients available for the plant.

Allow the soil to become dry for a period of several days to determine if your plant will recuperate.

Leaves Curling On The Bottom

If you have noticed the leaves on the bottom of your tomato plants curling, it may be a sign of a micronutrient deficiency in the soil.

Before the curling happens, however, the yellowing of the leaves indicates that there is something wrong going on already.

Common deficiencies include iron, zinc, and manganese.

Leaves Curling On The Top

 If you notice curly, small, and wiry patterned leaves on the top of your tomato plant, it may be suffering from a viral disease called curly top virus, transmitted by the leafhopper bug.

Once a plant is infected, it is best to remove it from the garden to prevent the virus from spreading to other healthy plants. However, you can still harvest the fruit from the infected plant.

Additionally, if mainly the young leaves are twisted and curled, it can also be a sign of herbicide damage.

Why Are My Tomato Leaves Curling?

Basically, there are 3 main groups of factors that cause tomato leaf curl or roll:

1. Environmental stress causing physiological leaf curl: this is the most common type of leaf curl.

The stress can be due to a number of reasons such as excessive moisture, high temperatures, insufficient water, severe pruning, strong wind, too much nitrogen in the soil, or root damage.

Physiological leaf curl first affects lower, older leaves. The leaflets curl inward while remaining green and thick.

  1. “The good news is that, as alarming as physiological leaf curl might appear to be, the disorder appears to have little detrimental effect on yield.” 

David Trinklein, University of Missouri

2. Herbicides: Tomatoes are rather sensitive to herbicides. Off-target drift of herbicides or contaminated compost damage often results in leaf curl and downward bending of the petioles and cupping of the leaflets.

New growth is usually affected first and symptoms may vary depending on the herbicide.

3. Viral diseases: Abnormal growth is a common symptom of many virus diseases. Tomato plants can be affected by several virus diseases, like curly top, which cause twisted growth of young leaves.

The curling is often random and not patterned.

Now let’s see the different reasons for tomato leaf curl in detail and how to fix them.

1. Transplant Shock Or Early Environmental Shock

If you plant tomatoes too early, it can cause their leaves to curl. This is because tomatoes are sensitive to low temperatures and thrive in warm soil and air.

When planted too early, the soil may still be too cold for the plant to establish a good root system, causing transplant shock.

This can stress the plant and make it struggle to grow, leading to curling of the leaves upwards and lengthwise.

How To Fix Transplant Scock

It’s important to properly harden off your tomato seedlings before transplanting them into the garden.

This means gradually acclimating them to outdoor conditions by placing them outside for short periods (for the first few days, avoid direct sunlight) and then bringing them back in, with each exposure lengthening before transferring them to the garden.

Before transplanting, it’s better to wait until daytime temperatures consistently reach above 70 °F (21 °C), and nighttime temperatures are no lower than 60 °F (15 °C).

2. Heat And Drought

They are the most common reasons. 

High temperatures, many times combined with too much sun exposure, can cause the leaves of tomato plants to curl up and become dry and brittle.

When tomato plants are exposed to excessive heat, they stop absorbing water and nutrients from the soil, which can lead to a lack of water and essential minerals in the plant’s system.

As a result, the leaves will start to curl up and inwards lengthwise as a means of conserving water and protecting themselves from further drying.

Drought is another environmental stressor that is closely related to heat stress. When the soil becomes too dry, the lack of moisture can cause the leaves to curl and wilt.

This is because the plant is not able to take up enough water to keep the leaves turgid, resulting in curling and wilting.

How To Fix Heat And Drought Damage

Providing some afternoon shade in hot or warm climates can help keep your plants from experiencing too much heat stress.

Make sure your plants are well-watered by providing at least 1 inch of water each week. It’s important to water slowly and deeply to promote deep roots and ensure even moisture levels throughout the soil.

Mulching around the base of the plants can also help maintain even moisture levels and keep the roots cool during hot weather.

3. Wind Damage

Wind can also be a factor that contributes to leaf curl in tomato plants.

“High winds, blowing dust and low humidity can damage the leaves and stems on tomato plants. Heat and low moisture can cause the edges of the tomato leaves to die back, then twist and curl.”

Texas A&M AgriLife Extension Service

This means that strong winds can cause dehydration and damage to the leaves, which can lead to curling.

How To Fix Wind Damage

You can shelter your plants from strong winds by using a shade cloth or planting them near a windbreak

4. Lack Of Water

Insufficient watering can cause the plant’s growth to slow down, with the leaves and stems appearing stunted, leading to leaf curl.

Correct watering means you keep soil moisture consistent. You need to water your plants deeply and evenly, making sure the soil is getting enough moisture.

Note: It’s essential to avoid overcompensating for underwatering by overwatering as this can lead to root rot.

How To Fix Insufficient Watering

Tomato plants generally require around 1 inch of water per week, although this can vary depending on environmental factors such as heat, water vapor in the air, and wind speeds. Water tomato plants deeply, allowing the water to penetrate the soil and reach the roots.

A good rule of thumb for watering tomato plants is to check the soil’s moisture level two to three times a week, particularly in warm weather. 

For a consistent supply of moisture, consider using drip hoses and mulching. 

5. Excessive Pruning

If too much foliage is removed, pruning can be a stress for the plant leading to leaf curl as a response. 

You must exercise caution when selectively pruning indeterminate tomato plants. Never prune off more than 30% of the total foliage from a tomato plant.

Note: determinate (bush) varieties don’t need any pruning.

How To Fix Too Much Pruning

If you have pruned your tomato plants too much, do the following to help the plant recover:

  • Water The Plant – By watering it well, you can ensure that the plant is receiving enough moisture to help it recover.
  • Let the Plant Recover – After watering and avoiding further stress, give the plant time to recover. As long as the roots are healthy, the plant should start to grow new foliage in a few days or weeks. Be sure to give it plenty of light, and keep it away from extreme heat or cold.

6. Nutrient Imbalance & Excessive Nitrogen

Tomato plants require a balance of essential nutrients to grow and produce healthy fruit. Over-fertilizing with nitrogen and other nutrients can lead to an imbalance in the plant’s system, causing leaf curling and other problems.

One common cause of tomato leaf curling is excessive nitrogen levels in the soil. Plants that receive too much nitrogen will exhibit symptoms such as upward curled leaves that are greener and thicker than usual, and the production of more foliage than fruit.

This is because nitrogen encourages leafy growth at the expense of fruit production.

How To Fix Nutrient Issues

For tomato plants that are experiencing excessive nitrogen levels and leaf curling, an effective solution is to cut back on fertilizer applications and supply the plant with less nitrogen until it has recovered.

This may involve switching to a fertilizer with a lower nitrogen content or simply reducing the frequency of application.

Micronutrient deficiencies, such as a lack of iron, zinc, or magnesium, can be remedied by adding fresh compost to the garden beds or using a fertilizer that includes these micronutrients.

Fresh compost can supply these necessary micronutrients to the soil and promote healthy plant growth without the risk of overfertilizing.

7. Herbicide Drift And Weed Killers

When herbicides and weed killers are sprayed on nearby plants, they can drift through the air and settle on the leaves of tomato plants.

This can cause a range of issues for the plants, including stunted growth, reduced fruit yield, and changes in appearance, such as downward and twisted leaf curling, yellowing, or browning.

Some of the most common herbicides known to cause damage to tomato plants include glyphosate, 2,4-D, and dicamba.

These chemicals can spread through commercial spraying, feed, and compost, which can be harmful to plants that come into contact with them.

How To Fix Herbicide Drift

It’s important to determine the severity of the damage caused, as mild exposure requires less intervention than significant exposure.

In severe cases where the damage is extensive, it’s advised to pull out the entire plant, including the roots, and replace it with a new one.

To prevent future herbicide drift, avoid treating your plants on windy days. Always read the labels of the herbicides and follow the application instructions carefully, and determine the wind direction before spraying your plants.

8. Herbicide Residue In Mulch And Soil

Mulch and soil are commonly used in tomato planting to conserve moisture, maintain soil temperature, and suppress weed growth.

However, if these materials are contaminated with herbicide residue, it can have devastating consequences on tomato plants.

There are several possible sources of contaminated mulch and soil, including hay, grass clippings, manure, and compost from a third-party source.

These materials may contain herbicides such as aminopyralid and clopyralid, which can remain active in the soil for several months to years after their application.

Symptoms of herbicide poisoning in tomato plants may include downward curling of leaves, stunted and twisted new growth, unchanged coloring, and affected other broadleaf plants in the garden.

How To Fix Herbicide Residue

First, identify the source of the contamination. Contaminated manure, compost, or mulch may be the cause of herbicide residue in your garden.

It’s best to create your own compost from known sources and ask hay suppliers about the use of aminopyralid or clopyralid in their products.

Activated charcoal or biochar can be effective in reducing herbicide residue in your soil.

Add activated charcoal or biochar to the soil to absorb herbicides or reduce the amount of contamination. Use 1 pound (approx. 0.5 kg) of activated charcoal or biochar per square yard (approx. 1 sq meter) of contaminated soil.

If the herbicide contamination is severe and cannot be fixed by adding activated charcoal or biochar, the best solution is to remove the contaminated soil and replace it with new soil free of herbicide contamination.

9. Tomato Viral Infection

Some of the most common viruses that infect tomato plants and cause leaf curling include

  • Tomato Yellow Leaf Curl Virus (TYLCV),
  • Tomato Mosaic Virus (ToMV),
  • and Tomato Spotted Wilt Virus (TSWV).

These viruses can be transmitted through infected plant material or insects like whiteflies, thrips, and aphids.

The symptoms of these viruses can vary depending on the specific type of virus and how advanced the infection is.

In the case of TYLCV:

“Symptoms in tomato plants are the upward curling of leaves, yellow (chlorotic) leaf margins, smaller leaves than normal, plant stunting, and flower drop. If tomato plants are infected early in their growth, there may be no fruit formed. Infected plants may appear randomly throughout the garden.“

hgic.clemson.edu

ToMV can cause mosaic patterns on the leaves, stunted growth, and reduced fruit yield.

TSWV can cause yellowing and wilting of the leaves, as well as a variety of other symptoms like ring spots on the fruit.

How To Fix Virus Problems That Cause Leaf Curl

To fix virus problems causing tomato leaf curl, the first step is to identify the virus causing the issue.

TYLCV is typically transmitted by whiteflies, while ToMV can be spread through contact with infected plant material or tools. To avoid transmitting the virus through human handling, it’s important to wash your hands or glove them before tending to the plants.

Once the virus has been identified, steps can be taken to reduce the risk of infection and limit the spread of the virus in the garden.

To reduce whitefly feeding that causes TYLCV, reflective mulches or oil sprays can be used.

It’s also important to remove infected plants and bag them for disposal at the end of the growing season.

10. Broad Mites

These mites are so small that they cannot be seen with the naked eye as they are 1/130 in (0.2 mm) long.

If you notice stunted growth, twisted, deformed, and curled leaves, and slight yellowing then browning in your tomato leaves, your plant may be suffering from infestation by broad mites.

Broad mites feed on the underside of the tomato leaves, causing them to curl downward and become distorted.

What To Do With Broad Mites

Act quickly to prevent the spread of the pests and minimize the damage to your crop. Here are some steps you can take to address broad mites on your tomato plants:

  1. Remove infected leaves, flowers, and fruits
  2. Use a sulfur-based miticide spray
  3. Avoid over-fertilizing (broad mites are attracted to vigorously young foliage, which can be caused by over-fertilizing)
  4. Keep the surrounding area clean and weed-free
  5. Introduce predator insects like lacewing and ladybugs

FAQ On Tomato Leaves Curling

What Does A Normal Tomato Leaf Look Like?

When looking at a healthy and normal tomato plant, you will notice that the leaves are a lush, vibrant shade of green. The leaves should be open, allowing for plenty of sunlight and air circulation to reach all parts of the plant.

While some of the longer leaves may appear slightly droopy, they should not exhibit any curling or abnormalities in coloration or stem appearance. Also, the presence of new growth and flowers on the plant is a positive sign of healthy development.

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AUTHOR

I'm a keen hobby gardener. I love growing fruits and vegetables, especially tomatoes. I'm also a certified instructor of the Square Foot Gardening Foundation.