Tomato leaves curling: causes and what to do

The most common reason tomato leaves curl is benign: physiological leaf roll caused by heat, water stress, or high fruit load. The second most common is overwatering. Herbicide drift and viral disease are less common but serious. The key diagnostic question is whether the curling

Curling tomato leaves are among the most panic-inducing symptoms because they look dramatic. But most cases of leaf curl are either harmless or the result of simple environmental stress. This guide walks through the five causes in order of likelihood.

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The five causes of tomato leaf curl

Cause 1: Physiological leaf roll (most common — benign)

Physiological leaf roll is the most common cause of tomato leaf curling, and it is not a problem. Per Penn State Extension, "physiological leaf roll in tomatoes is a normal response to environmental stress and does not affect plant health or yield."

What it looks like: Lower leaves roll upward along their length (like a taco curling) while remaining green and firm. The rolling is most pronounced on the lower and middle leaves. The plant looks healthy otherwise — no discoloration, no spots, no wilting.

When it occurs: Per Penn State Extension, "leaf roll is most common in mid-to-late summer during periods of high temperature, low humidity, or when the plant is carrying a heavy fruit load." Indeterminate tomato varieties are more prone to physiological leaf roll than determinate types.

What to do: Nothing. Per Penn State Extension, physiological leaf roll "does not require treatment." Mulching to conserve soil moisture and consistent watering reduce the stress that triggers it, but even well-watered tomatoes roll their leaves on the hottest days.

Cause 2: Overwatering

Overwatered tomatoes can show leaf curl along with yellowing, soggy soil, and eventually root rot. The curling from overwatering is different from physiological roll — leaves curl downward at the edges rather than rolling up along the midrib.

Per NC State Extension, "overwatered tomatoes show downward cupping or curling of leaves" combined with yellowing and poor growth.

How to confirm: Soil is consistently wet 2–3 inches below the surface. Leaves may be curling and yellowing simultaneously. If you dig around the roots, they may show signs of rot (dark, soft tissue).

How to fix: Reduce watering frequency. Allow the top inch or two of soil to dry between waterings. Improve drainage if the garden bed has standing water. See our article on tomato plant care for proper watering guidelines.

Cause 3: Herbicide drift

This is the most serious environmental cause. Several common lawn herbicides — particularly 2,4-D and dicamba, used in broadleaf weed killers — cause distinctive leaf distortion in tomatoes when the plants are exposed to even trace amounts.

What it looks like: Per UC IPM, herbicide exposure causes "cupping, twisting, and strapping of new growth" — the newest leaves and growing tips are deformed, often with a distinct downward cupping and narrow, strap-like leaf shape. This is different from the clean, uniform rolling of physiological leaf roll.

How to confirm: Per UC IPM, "new growth showing cupping, twisting, and strapping after herbicide applications in the area is strongly suggestive of herbicide exposure." Ask neighbors about recent lawn applications. Note wind direction on application days.

What to do: Per UC IPM, "if exposure was minor, new growth may appear normal as the plant grows out of the damage." Severely exposed plants may not recover. There is no treatment. Prevent future exposure by covering tomatoes with floating row cover on days when lawn herbicide applications are being made nearby.

Cause 4: Broad mite (Polyphagotarsonemus latus)

Broad mites are microscopic — invisible to the naked eye — and cause distinctive distortion of tomato growing tips. Per UC IPM, "broad mite damage causes downward curling, bronzing, and hardening of young leaves" at the growing point.

What it looks like: New growth at the shoot tip is stunted, hardened, and curled downward. Leaves may have a bronze or russeted appearance. The growing tip looks stunted or aborted. This damage pattern at the tip is distinct from the lower-leaf rolling of physiological leaf roll.

How to confirm: Examine the growing tips under a magnifying glass (10–15x). Per UC IPM, "broad mites are extremely small and require 20x magnification to see." Send a sample to a plant diagnostic lab if you suspect broad mites.

How to fix: Per UC IPM, "sulfur sprays are effective against broad mites" but must be applied carefully — sulfur can damage plants when temperatures exceed 90°F. Abamectin (Avid) is an effective miticide for severe infestations. Per UC IPM, "removing and destroying affected growing tips slows the spread."

Cause 5: Tomato yellow leaf curl virus (TYLCV) and other viruses

Viral infections cause leaf curling combined with yellowing, stunting, and overall plant decline. TYLCV is transmitted by silverleaf whiteflies; other viruses are spread by aphids or mechanically.

Per Penn State Extension, "tomato yellow leaf curl virus causes upward cupping of leaves combined with yellowing of leaf margins and interveinal tissue, reduced plant size, and poor fruit set."

What it looks like: Small, cupped, pale yellow leaves — especially at the growing tips. The entire plant is often significantly smaller than healthy plants. Flower abortion and poor fruit set are common.

How to confirm: The combination of cupping, yellowing, stunting, and poor fruit set distinguishes viral infection from the other causes. A plant with only leaf roll and no other symptoms is not viral.

What to do: Per Penn State Extension, "there is no cure for viral diseases in tomatoes." Remove and destroy infected plants to reduce the virus reservoir. Control whitefly populations with yellow sticky traps and insecticidal soap to reduce transmission. In areas with high TYLCV pressure (Florida, Gulf Coast, California), plant TYLCV-resistant varieties.

Diagnostic flowchart

1. Is the curling on lower/middle leaves only, leaves are green and healthy-looking?

→ Physiological leaf roll. Benign. No action needed.

1. Is the soil wet and the curling on all leaves with some yellowing?

→ Overwatering. Reduce irrigation; check drainage.

1. Is the new growth distorted, hardened, cupped downward, or bronze-tinged at the tips?

→ Broad mite or herbicide drift. Check for recent herbicide applications; examine growing tips.

1. Did new leaf distortion follow known herbicide applications nearby?

→ Herbicide drift. Grow out; prevent future exposure.

1. Is the whole plant small, with upward-cupping pale yellow leaves and poor fruit set?

→ Viral disease. Remove plant; control whitefly vectors.

Distinguishing physiological roll from other causes: the critical test

Common mistakes

Frequently asked

Is it normal for tomato leaves to curl in hot weather?

Yes. Per Penn State Extension, "physiological leaf roll in summer heat is a normal adaptation" that reduces water loss. If lower leaves curl during the hottest part of the day and uncurl in the morning or evening, this is benign. If leaves are permanently rolled and show additional symptoms (yellowing, spots, distortion), investigate further.

Should I remove curled leaves?

Remove leaves only if they show signs of disease (spots, lesions, yellowing with spots). If the leaves are green and otherwise healthy, curling alone is not a reason to remove them. Per Penn State Extension, green photosynthesizing leaves should be left on the plant.

Can tomato leaf curl spread to other plants?

Physiological roll, overwatering, and herbicide damage are not contagious. Viral diseases can spread to other susceptible plants in the nightshade family (peppers, eggplant) through insect vectors. Broad mites can spread to adjacent plants. If you suspect virus or broad mite, quarantine the affected plant and control insect vectors.

Sources

1. Penn State Extension — Tomato Physiological Leaf Roll
2. NC State Extension — Tomato Disorders
3. UC IPM — Tomato Viruses and Mite Damage