Downy mildew was first reported in the United States in 1880 and was first reported on roses in 1862 in England. The reproduction and spread of downy mildew fungi are rapid and their diseases can cause heavy losses in short periods of time and on a large number of different plants including vegetables, ornamentals, shrubs and vines. Symptoms of downy mildews occur on leaves, stems and flower petals. Infections are generally restricted to young, apical plant growth. Leaves develop purplish red to dark brown irregular spots, followed by yellowing of leaves. Leaf abscission may be severe and foliar symptoms in some plants may resemble burns from pesticide toxicity. In roses the severity of leaf abscission results in a spectacular dropping of leaves.
Under cool and humid conditions, grayish spore masses appear in large quantities on the lower surfaces of leaves; whereas, powdery mildews appear
mainly on the upper leaf surfaces. Roses and many other plants are unaffected by downy mildews when the humidity is less than 85%and temperatures
above 65 F. The optimum temperature for spore germination is 65 F and the spores germinate within 4 hours in a film of moisture on leaves.
Plant spacing aids in preventing moisture build-up on leaf surfaces caused by humidity, dew, plant watering and sprinkling.
Sanitation is important to prevent seasonal carry-over of the pathogen since it may over-winter in infected leaves, stems and flowers.
Spraying every 2 weeks with a broad spectrum fungicide such as GreenCure® aids in the prevention of the development of downy mildews.
GreenCure is very effective at treating and controlling Downy Mildew on Hops. Learn more about Downy Mildew on Hops.
Leaves infected with downy mildew