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When the foliage of your tomato plants doesn’t look normal, understanding the reasons is key to fixing the problem.
Reviewed by David McKinneyKey Points
- Reasons for tomato leaf curl are heat stress, lack of moisture, excess pruning, transplant shock, or herbicide drift.
- Give the plants proper care, including watering and mulching, and avoid the use of herbicides or contaminated compost.
- Viral diseases causing leaf curl require plant removal; prevent future issues by selecting disease-resistant varieties.
Tomato leaves curling is a warning sign that you should not ignore. To produce the loads of delicious homegrown tomatoes you anticipate, it takes a healthy plant with lush foliage. But your harvest could be at risk when you see leaves curling on your tomato plants. Curled-up leaves indicate that something is not right in the environment or within the plant itself.
To help you determine what is ailing your tomato plants, we have asked an expert about common culprits such as insufficient moisture, herbicide drift, and diseases. We also tell you the best course of action for each problem.
Meet Our Expert
Dr. Ajay Nair is a professor and the chair of the Department of Horticulture at Iowa State University.
1. Tough Growing Conditions
Nature can throw a variety of challenges at tomato plants as they grow. Less-than-ideal growing conditions are the most common cause of tomato leaves curling and the easiest to remedy. “Leaf curl is primarily driven by hot weather, lack of moisture, and heat stress, “ says Dr. Ajay Nair, Professor of Horticulture at Iowa State University. In overly hot and dry conditions, the leaf margins roll upwards. Nair says that you’ll usually see curling more on the lower leaves.
The science behind this stress-induced leaf curl reveals that it’s a way that plants actively protect themselves. When hot, dry conditions persist, tomato plants cannot take up as much water as they lose through evaporation. This internal water deficit causes leaflets to curl up. A curled leaf absorbs less of the sun’s energy and loses less water. Leaf curl is a self-defense mechanism.
What to Do
Reducing environmental stress that causes leaf curl can help the problem and prevent it too. Start with good watering practices. Aim to provide tomato plants with 1 inch of water a week. If plants don’t receive the required amount from rainfall, supplement by delivering water directly to the root zone with a hose or drip line. Avoid overhead watering to prevent the spread of disease. Add a 2-inch layer of mulch around tomato plants to limit soil moisture evaporation.
Tomato leaves curling brought on by harsh growing conditions usually resolves when the conditions improve. Don’t worry about long-term effects. A short battle with leaf curl “does not significantly reduce plant growth or yield,” says Nair.
2. Too Much Pruning
While pruning tomato plants helps promote fruit development, it causes problems when too much foliage is removed at once. The plant senses the sudden loss of energy-generating leaves, resulting in the remaining tomato leaves curling as a stress response.
What to do
The best remedy for excessive pruning is to water the plant well and give it time to recover. Let new leaves grow freely. The plant should return to good health in a couple of weeks.
3. Transplant Shock
Moving seedlings or young starts into your garden stresses tomato plants. Some tomato varieties curl their leaves in response to temperature fluctuations and root disturbance associated with transplanting.
What to Do
After leaf curl caused by transplant shock, plants often recover on their own within a couple of weeks. Provide plenty of water as your tomatoes settle in.
To minimize transplant shock in the future, make sure to harden off seedlings before planting and gently handle the root ball. Do your transplanting on a cooler, overcast day, or give your newly transplanted tomatoes some temporary shade with a tarp or other material that will block direct sunlight.
4. Weed Killer Damage
A weed-free lawn nearby could be the reason for tomato leaves curling. “Off-target drift of herbicides such as 2,4-D or dicamba is a frequent offender,” says Nair. If the wind blows weed killer onto your tomato plants, the chemicals will affect foliage growth and may even kill your tomatoes. Plants with herbicide injury have leaves that bend downward, and the individual leaflets bend upward in a cup-like shape. This looks different than the tightly curled or rolled leaves caused by hot, dry growing conditions.
Another source of herbicide-related leaf curl is contaminated compost or mulch. Nair says the contamination comes from long-lived pasture herbicides such as picloram, clopyralid, or aminopyralid within the commercially available compost materials. If you spread this compost in your garden, it may impact your tomatoes (and other plants).
What to Do
There is no cure for herbicide-induced leaf curl. Take a “wait and see” approach. Some plants will overcome the effects and produce a crop. Other plants will die without fruiting.
In the future, avoid using weed killers near tomato plants. Know the source of your compost and mulch, making sure to purchase from a reputable dealer.
5. Tomato Diseases
Though not very common, some viral tomato diseases could be why you’re seeing curling leaves. Some of the diseases affecting tomato plants include septoria leaf spot, a result of very wet conditions; early leaf blight, which appears after the plants have set fruit; and blossom drop, caused by extreme weather conditions causing both high heat and cool temperatures,
If a virus is to blame, you’ll see twisting and twining new growth instead of curled older leaves, which is typical for plants stressed by tough growing conditions. Individual new leaflets often curl due to diseases.
What to Do
There is no cure for tomato viruses. Remove the entire plant from the garden and dispose of it in the trash to prevent the virus from spreading. In the future, choose newer varieties that offer disease resistance to viruses.
Read the original article on Better Homes & Gardens
