Erysiphe cichoracearum

Fungal Disease

Erysiphe cichoracearum

Fungal Disease

Erysiphe cichoracearum

Fungal Disease

During warm, humid weather the powdery mildew fungus may produce over 2 million microscopic spores (conidia) on a square inch of leaf surface within a week or ten days (Figure 2). These spores, which are borne in chains, may be blown many miles in mild, moist air to infect vine crops. Thrips and other insects and farm equipment may disseminate the spores locally from leaf to leaf and from plant to plant.

The normal period between infection and the appearance of symptoms is from 3 to 7 days, or longer if weather conditions are unfavorable for the fungus. Infection and production of conidia occur most readily at about 81 F (27 C). The minimum and maximum temperatures are 50 and 90 F (10 and 32 C), respectively. The powdery mildew fungus is influenced greatly by plant age, humidity, and temperature. The fungus can reproduce under quite dry conditions with infections taking place with a relative humidity as low as 46 percent. The incidence of infection increases as the humidity rises to 90 percent or more, but does not occur when the leaf surface is wet.