Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
With the wet, cloudy weather we are seeing some edema on cole crops such as cabbage.
Edema is water blistering on cole crop leaves. The most common cause of edema is the presence of abundant, warm soil water and a cool, moist atmosphere. Under these conditions the roots absorb water at a rate faster than is lost through transpiration. Excess water accumulates in the leaf, some parenchyma cells enlarge and block the stomatal openings through which water vapor is normally released from the plant; thereby contributing to further water retention in the leaf. If this condition persists, the enlarged cells divide, differentiate a cork cambium, and develop elongate cork cells externally to form a periderm. The rupture of the epidermis by the enlarged inner cells and the periderm account for the raised, crusty appearance of older edema spots.
Edema on cabbage leaf.
Photo by Gerald Holmes, Valent USA Corporation, Bugwood.org