From his early days, Brandon helped his grandmother in her garden. He has always been passionate about tomatoes.
The Infamous Tomato Leaf Curl
Tomato plants respond to stress and diseases in different ways, one of the most obvious being the curling or rolling up of their leaves. If you notice that the new leaves (or maybe all the leaves) of your tomato plant are curling up, it is recommended that you investigate your plant and its surroundings to determine the cause of the problem. You should do this quickly because these problems are mainly caused by factors that eventually affect the flowering and fruiting of the plants.
Common Causes of Tomato Leaf Curl
Some of the common causes of tomato leaf curl are listed below, and an explanation of each follows:
- External stress
- Non-parasitic leaf roll
- Tomato yellow leaf curl virus
- Broad mites
One easy way to prevent leaf curl is by planting tomato species that are meant to grow in your climatic conditions and also by selecting disease-resistant varieties. But if you've encountered this problem, not all hope is lost; in most cases, curling can be fixed, and the tomato plants can recover and bear fruit.
External Stress (From Temperature or Watering Issues)
Leaf curl that is caused by external stress factors is more likely to be found in potted plants and those grown in grow bags. Leaf roll is found on tomato plants in wet and cool conditions. Inconsistent watering and pruning are also factors that could lead to curling.
If it's just the lower leaves that begin curling upwards on the edges, forming a cup, one possibility is that the soil is too soggy. It is therefore important that you allow the top of the soil to be dried out a little before you water again. Freely water plants in pots with drainage, but do not allow water to sit in the collecting tray at the base, because this can lead to root rot. Following the best practices when watering tomatoes helps prevent a lot of problems
Note: When the curling of the leaves is caused by external stress factors, the plants often continue growing and outgrow the condition, allowing them to flower and fruit well.
Non-Parasitic Leaf Roll (Irregular Irrigation and/or Bad Pruning)
Non-parasitic leaf roll is a kind of physiological leaf roll where the leaf tends to roll inward. In extreme cases, the leaves roll to an extent where they begin to overlap, making it appear to be a serious issue. It is usually caused by irregular irrigation and bad pruning. The plant usually recovers from this shock very quickly and you don't have to worry about it, provided you begin watering deeply and consistently and follow good pruning techniques.
You know your plant suffers from this kind of leaf curl when the problem begins with the leaves folding upwards, forming little cups, and then curl even more so that the new leaves seem to be overlapping each other. You would notice this issue on all the leaves of the plant.
The good news though is that the plant growth is not really stunted or hindered by this condition and you're not going to see any effects on the fruit. This issue is rectified after pruning and following correct watering techniques (deep, regular watering) after the plant has recovered from the shock. Pruning is good when done right.
In almost all cases of leaf roll due to herbicides, it is not the gardener but a neighbor who uses herbicides which are carried over by the wind. The culprit is almost always a lawn herbicide and it is usually phenoxy types like 2, 4-D.
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The tomato plant is susceptible during all stages of growth. A sign that the curling may be caused by herbicides is when the leaves curl downwards and pucker. In extreme cases, the stems become stiff and a whitish layer forms on them. The tips of new leaves will be elongated and leaf veins turn lighter and seem to be parallel when compared to older, unaffected leaves.
If your plant is already fruiting during this stage, the fruit turns out to be pointy and is usually harder to pick from the plant. You may have to chop it off and not just twist and remove.
You can prevent this by not using lawn clippings that come from lawns that were treated with herbicides. For mild cases, water the foliage of the plant to wash off the herbicide. Make sure you do not water when the sun is up.
Tomato Yellow Leaf Curl Virus
Not a very innovative name, the tomato yellow leaf curl virus (TYLCV) was identified in 2007 and there was an extensive program put out to educate farmers as its occurrence was common in greenhouses and not open gardens. This does not imply that it does not occur in open gardens, it does. The virus is spread by Whiteflies which feed on tomato plants. If you've heard of this virus spreading in your region it would be best to not plant tomatoes close to other crops that Whiteflies love, such as peppers.
The affected plants suffer from stunted growth and the edges of the leaves curl upwards, with the leaves themselves being yellowish and deformed. Plants that are affected by this virus are best removed and burned because they do not fruit as blossoms drop. The early signs are different though. The first leaves soon after an infection cup downward. If your plant is affected after the fruit has already formed, the fruit will continue to grow and will ripen too.
Tobacco Mosaic Virus
A more common occurrence is the Tobacco Mosaic Virus (TMV) which causes the leaves to be deformed with light and dark green mosaic patterns on the leaves with the leaves curling upwards if they curl. They do not always curl with the TMV. If your plant is infected you will notice a stunted growth and the blooms may have brown streaks.
There is no real cure and the virus is capable of living outside its host for a while and is mildly resistant to heat. Unlike the TYLCV that is spread through Whiteflies, the TMV is spread through contact. If you, therefore, notice that a plant has this problem, uproot it and any in the vicinity and bury deep or burn the plant.
Broad mites are sensitive to light and are usually present on the underside of tomato leaves and flowers. While they feed they inject toxins into the plant which distort the leaves.
You would not really notice a problem if broad mites are feeding on your plants unless the infestation is severe. In such cases, if you notice a distortion of young leaves and flowers look underneath for bronzed marks. You will not be able to spot the broad mites with your naked eye as they are really small at around 0.15 - 0.30 millimeters. If you do spot them using a microscope, they will be oval shaped and be either yellow or yellow with a tinge of brown.
Broad mites are either transported on the backs of Whiteflies or you can get them through transplants you buy from a local greenhouse. In case of severe infection, you may have to pull out your plants or alternatively consult an expert to confirm that it is, in fact, broad mites and begin using some sulfur-based miticides. It is best to consult an expert because you're also going to need to know whether your tomato variety is capable of withstanding the miticide you use. If you want to know more about broad mites in general, check this out.
Other Causes for Yellowing of the Leaves
It is also a possibility that your tomato plant just has yellow leaves and not a yellow leaf curl. There are plenty of reasons for this to happen and I have covered the major causes in my article on yellow tomato leaves.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.