Why do tomato leaves curl? (How to prevent it for good)


two red tomatoes on the plant

Gardeners are often concerned about any changes in their plants. TOMATOES are susceptible to viruses and environmental conditions. Have you noticed your tomato leaves starting to curl? It could be a result of biological, chemical, or environmental factors.

Extremes of temperatures cause tomato leaf curl. Too hot, too cold, or very dry or very wet. To combat Tomato leaf curl, grow indoors, ensuring constant temperatures and adequate moisture is available to the plants during the initial stages of growth.

Tomato leaf curl can at times affect the newly developing leaves or all the plant leaves. The curling usually starts with a few leaves then progresses to the entire plant. Tomato leaf curl can also take different forms: they can curl upwards or downwards. There are many known causes for tomato leaf curl, and they include:

  • Damage from wind
  • Herbicide drift
  • Herbicide residue
  • Broad mite
  • Tomato viruses

This article will focus on these causes independently and their preventive measures.

Tomato leaf curl can be caused by damage from winds

Tomato leaves curl up due to high winds, which blow dust, causing low humidity and water loss through the leaf surface. The condition is usually called physiological leaf roll. It is also caused by other factors such as heat and low moisture. With this condition, the leaves curl up in self-defense to protect their surfaces from further moisture loss.

The intensity of leaf rolling determines the impacts of the same on yield and quality. In severe cases, the plant flowers may drop, lowering fruit formation. If the rolling is not extensive, the plant usually improves once the environmental conditions normalize.

When the leaves of the plant curl, they are less effective in manufacturing food for the plant. This is because the surface, which usually traps light for photosynthesis, is no longer exposed. As a result, plant growth gets slower. Additionally, wind can also cause low temperatures, which are not conducive to the plant’s development.

Moderate wind is necessary for the healthy growth of your plants. Some of the benefits of wind to your plants include sufficient air circulation, preventing moisture from developing on the foliage surface, causing fungal diseases on your plants, and pollination.

Wind also carries tomato blight spores and this is just as problematic. This blog post I wrote covers that disease in detail

Severe winds can, however, kill young tomato plants. For this reason, you need to protect your plants from wind damage. We will now look at some of the ways wind is likely to damage your tomato plants.

Gardening designs to prevent tomato leaf curl

The location of your garden is critical in preventing your plants from wind damage. As you make choices on where to set up your garden, you need to look into the intensity of the wind in that area. If the wind is a serious problem, you can set up your garden near a shield such as a wall, fence, or trees. If you can’t find a shield, then you have to create one.

Additionally, you can set up your garden in a way that the flow of wind is regulated. If you are growing your plants in a container, then it gets easier as all you need to do is relocate them to a less windy location. Growing your plants in a moving tray will make it easier to move them around.

Make use of windbreak during the garden design phase

This form of protection is usually temporary. It could be made of a piece of cloth, wire mesh fabric, or woven wood panels. As you use windbreak, make sure it doesn’t affect the plant’s access to sunlight. Also, certain windbreaks can cause the space within the garden to heat up, causing other problems such as diseases and high humidity levels, which affect the development of the plants.

Tomato leaf curl is a troublesome disease for tomatoes, but it is not the only one and if you are suffering from any other diseases check out the video below where I take you through everything you need to know about tomato diseases.

Herbicide drift which effect tomatoes

Low wind levels of 5 mph can carry herbicides for a mile, causing herbicide drift, severely damaging tomato plants. This occurs when herbicides used in the treatment of other plants such as cotton and corn land on the surface of your tomato plants.

Even broad-spectrum herbicide weedkillers for lawns such as glyphosate and the growth regulators can affect tomato plants causing these symptoms.

Tomato plants are pretty sensitive to these herbicides, and concentrations of as slow as low as 0.1 ppm can affect your plants. Even if your plants physically recover from herbicide drift, the yield is usually affected.

The leaves of TOMATOES already injured by herbicides such as 2,4-D can never be treated and will usually never recover. If the growing leaves are also affected, you need to harvest the fruit and get rid of the plant. However, recovery is possible for young plants with six weeks of harvesting. Nonetheless, if new buds don’t start showing improvement within a week, you should consider uprooting the affected plants and replanting.

How to protect your tomato plants from herbicide drift

Damages from herbicide drift are often irreversible, especially for older tomato plants. For this reason, the farmer or gardener should work on the following preventive measures to protect the plants from possible exposure:

  • Take note and follow instructions provided by manufacturers of herbicides, including the dosage.
  • Avoid the use of herbicides when it is windy, more so when the wind is blowing towards tomato plants
  • When using postemergence herbicides growing near tomato plants, always use a hooded spray
  • Always spray at low pressure to increase the size of droplets and reduce their ability to go with the wind
  • You can also spray at lower speeds to reduce the movement of spray in the air
  • Wherever possible, include spray additives.
  • Use the most appropriate spray nozzles for the chemical and always wash out all the chemicals from previous applications before and after using the spray tank.

Herbicide residue can potentially cause tomato leaf curl

Tomato plants are sensitive herbicides left in mulch and compost made from previously sprayed Grazon, GrazonNext, or GrazonNext HL. The chemical compound in these products is aminopyralid, and it can remain active for close to two years.

The same compound can also be transferred in manure from animals that feed on treated plants. Unfortunately, this compound is commonly applied in manure as it is used in pastures to kill broadleaf weeds.

Suppose you read the instructions on this product. In that case, you will realize that the plants collected from the sprayed fields are not suitable for vegetable manure.

Additionally, gardeners who sell hay or manure should notify buyers that they used the aminopyralid chemical. As a buyer, you also need to find out your hay or manure source and the type of chemical.

Preventive measures for your TOMATOES against herbicide residue

  • Avoid using aminopyralid-treated plant residues, haw or straws, within the 18month window period
  • In mushroom spawn, compost or mulch, avoid using manure from animals that have fed on treated forage or hay within the previous three days
  • Avoid planting tomato plants in fields treated with aminopyralid and manure that could contain the chemical product.
  • Aminopyralid breaks down faster with warm moist soil, watering compost and burning plant residues could speed up the herbicide decomposition process

A world without tomatoes is like a string quartet without violins.

Laurie Colwin

Damage from broad mites

Broad mites affect tomato plants, among other vegetables. They are 0.10 to 0.30 millimeters long, oval-bodied, and yellow to translucent. These organisms feed on the young leaves of TOMATOES and flowers in the absence of light. Since they are sensitive to light, broad mites commonly affect plants grown under a shade or in greenhouses.

As the pests feed, they inject the leaves and flowers with chemicals that distort and twist the plant leaves. It is difficult to diagnose this problem because the pests are invisible to the eye and are often missed under a magnifying glass. Moreover, the damage appears like any other on the tomato plant.

However, severely affected plants will have the leaf or fruit underside bronzed or rusted. For this reason, they are often discovered when the damage is quite extensive. You can look out for the eggs on the tomato leaves for early diagnosis, usually white, oval, and bumpy.

Broad mites develop and multiply fast, with eggs developing into adults within six days in hot weather and up to ten days in the cold. They are, however, affected by weather conditions such as sunlight, and for this reason, they will rapidly come and go.

Broad mites affect tomato plants from the legs and antennae of whiteflies whenever they land on them. You can also transplant infected plants from greenhouses. There is no possible recovery for severely damaged tomato plants. For this reason, the farmer needs to uproot and dispose of.

Treatment for broad mites

  • If the plants are moderately damaged, you can treat them with sulfur-based miticides- if the tomato cultivator is tolerant.
  • Additionally, you should avoid treating tomato plants when water-stressed or at a high temperature above 90F, as they can suffer further damage.
  • You can also use other compounds to treat broad mites such as Horticultural Oils and Insecticidal Soaps.
  • Predatory mites are the most effective as they provide a lasting solution to broad mite attacks.

Tomato viruses

There is a wide range of tomato viruses that can cause tomato leaf curl. Tomato leaves affected by viruses can be initially confused with phenoxy-based herbicide damage. However, as the disease progresses, yellow-green mosaic patterns start to form on the leaves.

The most common tomato viruses causing tomato leaf curl include those in the geminivirus group, such as the tomato yellow leaf curl virus commonly found in Texas. Whiteflies commonly transmit this form of the virus. Other tomato viruses that cause tomato leaf curl include:

  • Tomato yellow streak virus
  • Tomato yellow mosaic virus
  • Texas pepper virus
  • Sinaloa tomato leaf curl virus
  • Potato yellow mosaic virus
  • Pepper huasteco virus
  • Tomato leaf crumple virus
  • Chino del tomato virus
  • The tomato yellow leaf curl virus

Another major virus that tomatoes suffer from is Septoria Leaf Spot. This will kill the plants. In this article I wrote will show you how to identify it and all the remedies in order to treat it effectively.

If you are concerned about a virus infection in your tomato garden, look for new tomato varieties more resistant to viruses. Unfortunately, you will not find an utterly resistant cultivator.

The other option is by use of insecticidal oils and soaps to control whiteflies that cause tomato viruses.

tomato disease

Prevention of tomato viruses

Other possible causes include:

  • Transplant shock; this occurrence is expected due to root damage, and it occurs once you transplant your seedlings from the nursery.
  • Excessive pruning; pruning is helpful in some cases, but it can potentially cause stress to the plant due to more exposure to heat. Excessively pruned tomato plants can recover on their own.
  • Excessive nitrogen; too much nitrogen fertilizer applied during the fruiting stage can cause the leaves to start curling. At this stage, you should only use phosphorous and potassium fertilizers.

Conclusion

Tomato leaf curl is a sign that something is not okay, and you need to step in in time to save the plant. You need to identify the cause of the problem to manage it. Some problems such as physiological damages caused by wind will go away on their own depending on the severity.

Herbicide-related damages need to be avoided as they can have severe damage to the crop. As for broad mite and viruses, you need to control the causing agent, which is often whitefly. If you are unsure of the cause, you should seek professional help and lab analysis.

Tomatoes are great to grow especially if you follow the basic rules and growing methods. I wrote a detailed article on growing tomatoes at home to ensure perfect results every time. Read that here.

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Tony O'Neill

I am Tony O'Neill, A full-time firefighter, and professional gardener. I have spent most of my life gardening. From the age of 7 until the present day at 46. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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