Tomato leaf curling

Horticulture Hints

Due to our abnormal spring weather conditions, many questions have been received regarding plant health issues. One question in particular is that of tomato leaves which are curling up. Clients worry that the leaf roll may be due to chemical drift, disease or insects. But there can be several environmental causes that cause tomato leaves to roll or curl. Hot weather and drying winds can cause a symptom called physiological leaf roll. This is a plant self-defense mechanism, where leaves and leaflets curl slightly upward to prevent further water loss in response to harsh environmental conditions.

Physiological leaf roll in tomatoes is often seen as spring weather turns to summer. Mild spring weather at planting can cause vigorous top growth, even without adequate root growth; then when our tomatoes experienced unusually hot conditions, leaf rolling occurred.

If weather conditions cooperate and environmental heat stress is reduced, the plant can recover from mild leaf roll without out affecting yield. If hot conditions persist, plant stunting, blossom drop and quality of the fruit may be affected.

Excessive nitrogen, drought, severe pruning, root damage and transplant shock are also some other environmental factors that can cause physiological leaf roll in tomatoes.

Managing this problem can be done by following basic cultural methods such as the proper hardening off tomatoes before transplanting out to the garden. Planting different type cultivars, providing a consistent soil moisture, and maintain temperatures below 95 degrees by shading or evaporative cooling. Also avoid over-fertilization, excess pruning, and root damage.

Did you know? Tomato cultivars selected for high yields usually tend to be most susceptible to physiological leaf rolling. Indeterminate tomato cultivars are reported to be more sensitive to this disorder than determinate cultivars. Determinate tomatoes stop growing at first fruit set; indeterminate tomatoes continue to vine and grow, producing fruit until killed by frost.

Horticulture Questions? Contact McCormick at yvonne@iastate.edu for information or advice.

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