Powdery Mildew of Strawberries in Home Fruit Plantings

Symptoms and Disease Cycle

The disease is caused by the fungus Podosphaera aphanis var. aphanis.   

In mild cases, leaves curl inwards, giving the appearance that the plants are drought-stressed but without wilting. With further disease development, red to purple blotches appear on the leaves and some leaf tissue may die. A whitish "powder" is sometimes seen on leaves or fruit making the fruit color appear lighter than normal. If the fruit surface is colonized, the fruit does not expand as much as usual resulting in seeds that are abnormally raised and easily rubbed off. In very severe cases, flowers may become colonized and fail to pollinate.

Disease development is fastest when humidity is high and temperatures are moderately cool (not cold). The fungus is  is an "obligate parasite" which means it needs to reside in a living host for its survival. It can be found overwintering in old but living leaves.

Disease Management

Especially susceptible varieties include all day-neutral (everbearing) varieties, and the June-bearing varieties Earliglow and Darselect.  The use of resistant varieties and adequate row spacing aid in the control of this disease. Any practice that reduces humidity in the canopy such as keeping plantings weeded will help also.