Fungal powdery mildews can occur on most flowering plants. The disorder affects the foliage, stems and flowers of ornamental plants. The fungus spreads from plant to plant by spores. It prefers a temperature range of 60 to 80 degrees Fahrenheit. Powdery mildew does not require water to grow. The fungus does grow well in the shade and when overcrowding of the plants occurs.
The fungal infection appears as a white coating over the plant's surface. The coating resembles a fine dusting of powder. When the foliage of the plant is gently rubbed, the fungus will readily be removed. The leaves and buds of the plant appear distorted if the powdery mildew infection is severe. The fungus can invade the plant's cells and cause leaves to yellow. The fungus does remove nutrients from the plant, according to Cornell University.
Powdery mildew fungus spreads when it produces tiny white circular patterns of pure white mold on the leaf's surface. The circular white patches are the developing spores. Once the spores form, they are easily transferred from plant to plant by the wind. Powdery mildew is a common and widespread plant diseases, according to the Colorado State University.
The powdery mildew fungus spores spend the winter on the fallen leaves beneath the plant or other debris. Removing the dead plant life in the fall can help control the fungus the following spring. During the spring, the fungus springs back to life and spores are produced. The spores quickly infect the new plant's growth. Each powdery mildew fungus is species specific which means that only certain plant varieties will show infection, but other plants may appear immune in the garden. In areas with mild winters, the fungus does not overwinter but continues to grow and spread each month.
Carefully select a fungicide that is specific for the flowering plant that is infected with fungus. Apply according to the directions on the label for control of the powdery mildew. Apply the fungicide when the white fungus patches appear on the plant. Fungicides such as thiophanate-methyl, potassium bicarbonate and sulfur are widely available for prevention and treatment of powdery mildew fungus.
Many plant varieties offer resistance to powdery mildew fungus, according to the University of Minnesota. Consider planting them in areas with a high incidence of fungus. Prevent fungal growth by spacing plants adequately. Watering in the morning will also help the plants leaves to dry out before nightfall.