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Only a few of these events would result in a disaster , but all would be of essential scientific interest if we are to make significant progress in understanding the earthquake cycle . Spores produced on infected tissue are typically water-splashed or windblown to healthy geranium leaves , where they start new infections . The fungus survives on infected plant material kept indoors over the winter or in greenhouses . Powdery mildew can be a serious foliar disease in some years and some locations ; for control of powder mildew or another specific insect or disease pest , contact your county extension office . Tolerate and ignore fourlined plant bugs when possible , especially if you have not seen much damage in recent years . These sclerotia will be visible on the soil around an infected plant as well as on infected plant tissue . In the spring , leafhoppers feed on infected plants . Symptoms : Circular black spots ranging from 1/16 inch to 1/2 inch in diameter appear generally on leaves upper sides .