Downy mildew first shows itself on the leaves of infected plants. On most host plants, yellow or tan patches appear on the upper leaf surfaces; a fuzzy growth coats the undersides. The upper surfaces become darker as the disease progresses. The color of the growth varies depending on the type of plant. The oldest leaves, usually the ones closest to the ground, show the signs of powdery mildew first. Eventually the growth of the plants slows and it dies.

On turf grasses, small, yellow areas develop on the grass. Affected grass may be easily pulled out as its roots are shortened. A white, downy growth may be visible.

Many fungal organisms cause downy mildew on different species of plants. As with may fungal diseases, wet, crowded, or humid conditions encourage the development of downy mildew. Cool weather seems to encourage it as well. The spores are spread by air or water.

To control downy mildew, give plants plenty of space to encourage good air circulation. Reduce shade, pull weeds, and practice good garden hygiene by disposing of debris in fall. Avoid overhead irrigation of vegetable and ornamental plants; provide good drainage for lawns. Rotate crops; fungal spores can survive in the soil. Pick and destroy affected plant parts. For chemical control, Gulley Greenhouse carries Fertilome Systemic Fungicide. Fungicides will not reverse the disease, but may prevent further infection.