Geraniums are found in many yards and gardens. This flower is often placed in window boxes, flower beds or used as border plants. Geraniums thrive in areas of full sun and typically reach 12 to 20 inches in height. Geraniums are susceptible to a disease known as powdery mildew, which causes white fungus to grow on its stems, leaves and flower buds. While powdery mildew is not usually harmful to geraniums, it can become unsightly.
Almost every plant in the landscape can be affected by powdery mildew. This disease is caused by fungi and produces similar symptoms in most plants, trees and flowers. Warm, dry weather conditions promote the development of powdery mildew. Geraniums planted in shady areas may develop this disease because of the high humidity in areas of deep shade. Powdery mildew usually disappears when the temperatures rise in the summer.
Powdery mildew is characterized by a white or gray fungal coating on plants. This fungus has the fine texture of talcum powder, which is where the disease received its name. This disease affects the stems, leaves and flowers of host plants. Geraniums with powdery mildew may also exhibit symptoms of leaf distortion, leaf yellowing and disfigured flowers. While powdery mildew does not usually kill host plants, it can cause premature leaf loss and reduced vigor.
Preventing powdery mildew development is possible by purchasing resistant plant varieties. Consult your local nursery regarding mildew-resistant geraniums. Remove all diseased plant debris from your garden and destroy it. Shady areas promote powdery mildew, so plant your geraniums in an area that receives plenty of sunlight each day. Always water your plants early in the day, so they are totally dry before nightfall. Avoid handling wet foliage, as this can promote or spread disease.
Geraniums with powdery mildew may not require chemical controls unless severe symptoms are present. Some plants may suffer adverse effects from this disease, which warrants control measures. Fungicides are available for the treatment of powdery mildew. Spray your plants with fungicides frequently and more often if the weather is damp and cool. Always follow the directions on the manufacturer's label for best results.