Be on the look out for powdery mildew

Powdery mildew epidemics can occur without warning, report Mich. St. Univ. plant pathologists Mary Hausbeck and Blair Harlan. They said depending on how the disease is managed, will determine if it has minimal impact or results in complete crop loss. The white talcum-like growths, or colonies, are initially small but can rapidly blight the leaves, stems and flowers of susceptible crops. Some powdery mildews are caused by Erysiphe cichoracearum, which can infect many different annual and perennial flowers.
Powdery mildew can infect plants even when the relative humidity is low, but epidemics are prompted when relative humidity is high. Sometimes the powdery mildew progresses unnoticed until many plants are infected.
Growing crops susceptible to powdery mildew can be a challenge, and fungicides have typically played a key role. Powdery mildews have been known to genetically adapt to overcome some of the most effective fungicides.
Some plant species, including gerbera, verbena and begonia are very susceptible and should be sprayed more frequently with the most effective fungicides. Other plant species may not need frequent applications, but should be scouted regularly for signs of the disease.