Tomato Leaf Curl - Why Are My Tomato Plant Leaves Curling?

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In many gardens, the tomato patch is the pride and joy of every gardener. We’re not just talking about the landscaping aspects of its cascading bushes, but also the ruby crops that have a place in every cuisine. But as gardeners are well aware, tomato plants are not easy to grow and care for.

As much as we love tomatoes, pests favor the round and shiny tomatoes and sometimes would strike even before the flowers and little tomatoes have appeared. One of those diseases that makes every tomato gardener shudder is the tomato leaf curl. It’s more common than you think.

So what is it and how do you protect your precious tomato patch against it?

What Is a Tomato Leaf Curl?

The leaves of the tomato plant are very sensitive. You can think of them as the bush’s nervous system. When the plant is exposed to stressing elements either from the weather, an attack of bugs, or dry or malnourished soil, the leaves are the first to show signs of this stress. It might start with the new leaves but it soon spreads if the causes have not been addressed.

In the case of tomato leaf curl, the leaves do just that. They roll and curl as if in anguish. It’s a cry for help. A close look at the plant and what’s going on in its near vicinity should give you a clue as to what’s causing the disfigurement of the leaves. Then you can take action and resolve the issue. In many cases, the plant can continue to grow and produce crops. But in others, as with viruses, the disease might be fatal.

It is worth noting that not all tomato species are prone to leaf curl. Some have high resistance to the disease as well as many other infections that plague the plant. You can avoid this problem altogether by selecting the right seeds for your region and weather as we’ll see later.

Symptoms of the Tomato Curling Leaves

Even though the disease is called tomato leaf curl, the symptoms are not limited to the leaves twisting or curling up. Since there are many causes from pests to pathogens to weather conditions, the symptoms also differ. Here are the signs to look for and the reasons behind them.

Curling leaves: the most common symptom and luckily it’s a benign one. The leaves look shriveled and curled up as if they’re fending off an attack. In this case, the attack could be as simple as the changing temperatures at night or it could be a real assault by aphids.

Distorted/shrunk leaves: if you notice the leaf area is much smaller than usual or the leaves have a disfigured look about them, this can be a response to light or temperature changes. But more often than not a virus or contamination from a weedkiller causes this condition.

Mottled leaves: yellow and brown spots appearing on the surface of the leaf is a cause for concern. This could be a result of magnesium deficiency and a plant food supplement would take care of the problem. Note that this is only a problem if many leaves are mottled including young ones. Mottled older leaves shouldn’t be a concern.
Nodules and lumps: caused often by high humidity in the air or soggy soil. When the plant absorbs more water than it needs, it stores it in swelled water bubbles on the leaves. Adjust your irrigation or increase ventilation around the bush to alleviate the levels of humidity.

Why Are My Tomato Plant Leaves Curling? (Causes)

As the diverse symptoms of the disease show, the causes can be quite varied. In the case of tomato leaf curl, more than one cause combines to create the condition. So it’s prudent to keep an open mind and conduct an exhaustive investigation of the symptoms and possible causes to eliminate the problem. The four main causes of tomato leaf curl are

Weather damage

Many vegetables struggle with harsh weather conditions. From eggplants to tomatoes, a hot and dry spell can prove to be too stressful for the plants. Tomatoes in particular need the right condition for them to grow. Strong wind, hot weather, excessive dust, or pollutants in the air, can all be too much for the tomato bush to handle.

The heat poses a risk on the plant and to avoid the ravages of dehydration, the tips of the leaves die and curl up to preserve what little humidity the plant has in store. This is a self-defense mechanism and often improves on its own. The plant’s growth and yield don’t get impacted unless the stressful conditions continue for a prolonged duration.

Herbicide drifts and residue

In general, you should avoid exposing your tomato bushes to chemical herbicides. As we saw with extreme dry heat or excessive dust in the air, herbicides can have a similar impact on the leaves and even crops. If your garden is in the vicinity of farms where herbicides or weed killers are sprayed, the drift can cause the leaves of the plant to shrivel up as if you have sprayed them directly.

Another source of herbicides is the residue in compost and mulch. This is especially true of compost made from hay that was sprayed. Herbicide damage has a lasting impact on the yield even if the plant continues to grow in a seemingly normal manner.

Broad mite

You probably have seen broad mites (Polyphagotarsonemus latus) in action before if you have grown chrysanthemum, dahlia, pittosporum, zinnia, schefflera or other flowering plants in your garden.

The mites feed on the young leaves and stay away from the light. They inject a toxin in the leaves which causes them to curl up and get distorted. If the underside of the fruits or leaves has a bronze color, then you have a broad mite infestation.

A close inspection of the plant will reveal the broad mites on and around the young offshoots. Sometimes you can also see their white egg clusters on the leaves.

Tomato viruses

Notice we said tomato viruses and not a tomato virus. That’s because we’re talking about a whole litany of viruses that inflict their damage on the tomato plant.

The viruses fall under the geminivirus group and include

the tomato yellow leaf curl virus
pepper huasteco virus
chino del tomato virus
Texas pepper virus
tomato leaf crumple virus
tomato yellow streak virus
Sinaloa tomato leaf curl virus
tomato yellow mosaic virus
potato yellow mosaic virus

What makes the virus attacks hard to deal with is that the symptoms are often similar to those of herbicides where the leaves get twisted.

Only when patterns in green and yellow appear on the leaves would you know that this is a virus. By then the virus would have spread to the whole bush making it hard to control it.

Remedies for Leaf Curl in Tomato Plants

Since there are many causes for the symptoms and the disease, your approach to manage and treat the plants should be to counter the causes. There’s no silver bullet to deal with this disease. Most of the remedies work well if the cause of the problem is weather-related as opposed to a pathogen or a chemical herbicide. They fall under these categories.

Temperature and sunlight control: Shade and managing temperature can prevent the tomato leaf curl if you live in an area that gets harsh sunlight or extreme temperatures. Consider growing the tomato plants in a greenhouse and install a thermometer to monitor the temperature.
Regulate water: Too much water causes nodules and lumps to appear on the leaves. A dry soil would trigger the leaves to curl up in self-defense to preserve water in the plant. Water the plant if you notice the topsoil is dry. Don’t remove the lumps and nodules as they are needed to eliminate excess water.
Keep herbicides and weed killers away: this might be easier said than done especially if a neighboring garden uses the herbicides. But you shouldn’t store cans of weed killers near the plant and make sure the compost or mulch is herbicide-free before you apply it to the tomato pot or bedding.
Use sulfur-based miticides: these are pesticides especially targeting broad mites. Only use the miticide lightly and make sure the plant is well irrigated and the temperature is below 90 degrees Fahrenheit. Horticultural oils and insecticidal soaps are also effective against the mites.
Remove damaged plants: use this when the cause of the disease is one of the geminivirus group. To prevent the spread of the virus infection, pull out the damaged plants, and burn them. Monitor the rest of the plants to make sure they’re not infected.

Tomato Leaf Curl – Why Are My Tomato Plant Leaves Curling?