edema on romaine lettuce leaves

Edema on Romaine lettuce leaves

Updated: May 3, 2021

What causes small blisters or bumps on leaves?


the back of a pepper leaf with raised bumps
Scab-like blisters on the back of a pepper leaf

A physiological condition caused when plants take up water faster than it can be used and transpired. Excess soil moisture combined with cool temperatures, overcast weather, and poor air circulation can cause a buildup of water pressure within the leaves. Sometimes it develops during periods of warm, humid days with rainfall, and cool nights. The water pressure causes cells on the lower leaf surface to rupture, forming brown, corky, scab-like blisters. These spots are also visible from the upper leaf surface. Edema stops developing when the weather conditions change, but existing spots remain on the leaves. Prevent edema by allowing the top 2 inches of soil to dry between watering and space plants to allow for sufficient air circulation. Edema is most often seen in cabbage growing in waterlogged soil and in container tomatoes during wet spring weather.

severe case of edema on tomato leaves
Large blisters indicate a severe case of edema on tomato leaves