Symptoms often appear first on older leaves. If weather conditions are moist and temperatures are low, masses of gray to violet fungal spores envelop infected leaves, which become girdled, collapse, and die. The dead leaf tissue is rapidly colonized by purple blotch, which is dark in color and obscures downy mildew. Downy mildew seldom kills onion plants, but bulb growth may be reduced. Bulb tissue, especially the neck, may become spongy and the bulb may lack keeping quality.