Tomato plants are one of the easiest and most popular vegetables to grow. But a common problem is that tomato leaves often curl. Sometimes it only affects new leaves, but sometimes you may find all tomato leaves curling.
The reason tomato leaves curl may be biological, environmental, or chemical. For example, they may be attacked by a virus or mites. Wind, heat, and drought are all environmental issues that can cause leaf curls. Herbicides are the most common cause of chemical causes. But a nutrient imbalance may also result in tomato leaf curling.
Reasons why tomato leaves curl
If your tomato leaves curl, this does not necessarily mean that your plant will die. But it may. So, it makes sense to identify the cause and take corrective action as soon as possible.
The Texas A&M AgriLife Extension provides invaluable information in a publication, What Makes Tomato Leaves Twist or Curl? by Joe Masabni, Juan Anciso, and Russel Wallace. They highlight five main reasons for the twisted curl of tomato plant leaves.
- Wind damage
- Herbicide drift
- Herbicide residue
- Broad mite
- Tomato viruses
The wind is clearly an environmental reason, while herbicide damage is chemical, and broad mites and viruses are biological.
The biological causes of tomato twist curl are pests and diseases. The most common are tomato viruses, which we will discuss in a separate section, and board mites.
Broad mites avoid light and feed on the leaves and flowers of tomato seedlings. They inject toxins into the tomato leaves that make them twist and distort.
A major problem is that they are invisible to the human eye and even difficult to see under a magnifying glass. More often than not, you will pick up an infestation once the damage has been done.
Sometimes plants from greenhouses are infested. Otherwise, they may be spread by whiteflies.
If the infestation is bad, it’s best to pull up affected tomato plants and dispose of them. Do not put them into your compost heap or bin otherwise the mites will spread.
The most common environmental factor that leads to tomato plant leaves curling is wind. High winds can also damage the leaves and stems.
Drought and heat exacerbate the wind. When it’s very hot and there’s not enough moisture, tomato leaves will often twist and curl and often die back.
Hot dry weather also causes physiological leaf roll. This is simply a self-defense mechanism that helps to prevent them from even more water loss.
Another environmental cause is planting your tomatoes too early before they have hardened off. You also need to be sure the weather is warm enough for planting.
When tomatoes are overfertilized with nitrogen, the leaves sometimes curl upwards. Insufficient phosphorus can also result in tomato leaf curling.
In gardens where herbicides are in use, these can be the primary cause of tomato plant leaf curl. We mentioned two different types above.
Herbicide drift happens when chemicals are sprayed. Tomato plants are very sensitive to herbicides and they are easily injured.
Herbicide residue damage happens when the herbicide is left in compost or mulch that is made from manure or hay from fields that are sprayed.
Tomato Leaf Curling Virus
There are hundreds of viruses that stunt the growth of tomatoes and cause tomato leaf curls. Some are more virulent in certain areas rather than others.
For example, the tomato yellow leaf curl virus is the most common type in Texas. Other types include the tomato yellow mosaic virus and the tomato leaf crumple virus.
The tomato yellow leaf curl virus is transmitted by whiteflies. The edges of the leaves turn yellow and the undersides often go a purple color. Plant growth is stunted and fruit production is limited.
The tomato mosaic virus is spread by aphids. The leaves curl and become mottled. If the fruit becomes infected it will be brown inside.
Some types of tomatoes are more susceptible to damage than others even though there are new more resistant varieties.
How to help your tomato leaf that curls
If your tomato seedlings are attached by broad mites, you may be able to clean the leaves with insecticidal soaps or horticultural oils. Alternatively, you can introduce predatory mites that attack and eat broad mites.
You can use insecticidal soaps and horticultural oils to control some types of leaf curl viruses including tomato yellow leaf curl virus. An important way to prevent infections is to keep your veggie garden weed free.
Unfortunately, there isn’t a cure for the viruses that attack tomato leaves. The only solution is to pull them out and dispose of them.
How to prevent tomato leaves from curling?
The best way to prevent a tomato leaf from curling is to follow a simple management strategy. The University of Missouri Integrated Pest Management has this advice:
- Choose varieties that aren’t prone to plant leaves curling
- Ensure there is adequate moisture in the soil
- Don’t over-fertilize and be careful not to use fertilizers that are high in nitrogen
- Be conservative when you prune indeterminate varieties that are more vulnerable to leaf curl
- If possible, shade plants growing in high temperatures
These steps will help to reduce the environmental stress that causes what they call physiological leaf roll. But be aware of the other causes of environmental stress including those mentioned above, as well as severe pruning or root damage that may be caused by pests.
There’s not a lot you can do to prevent wind, heat, and drought conditions, but you can choose a sheltered spot. This will shield your plants from intensive sunlight and heat and provide some protection from strong, drying winds.
You can also mulch around the base of plants to maintain moisture in the soil.
As mentioned above, keeping your vegetable garden weed free will help to minimize the various types of leaf curl virus. This is because weeds often act as host plants for insects that transmit viruses.
You can avoid herbicide damage by avoiding herbicides and using organic products to kill weeds. Better still, pull them out manually.
The information in this article will help you if you find yourself asking, Why are my tomato leaves curling?
There are many reasons, and it will pay you to identify the cause. Then you can either treat it or remove the damaged plants and avoid the problem next time you plant tomatoes.