| General Recommendations: Downy mildew is a fungal disease of leaves and sometimes of pods and seed. The fungi that cause downy mildews as a group are considered to be obligate parasites, meaning that they are restricted typically to one specific host. The disease is more common on herbaceous plants and is favored by temperatures cooler than 65 degrees and by 100% relative humidity. Symptoms include the yellowing of leaves and the advanced development of white fungal growth on the undersides of older leaves. Because downy mildew symptoms are mild and generally restricted to older growth, they present few problems in the landscape. Downy mildew can, however, become systemic in small seedlings and lead to rapid death, however this is rare and more commonly associated with infected seed that has been planted. The two most important downy mildew diseases are those of snapdragon and of grape.
Control of Downy Mildew:
1. If plants are in a greenhouse, provide heat and ventilation to keep the humidity below 80%. Space plants for good air circulation and keep night temperatures above 50 F.
2. Avoid overhead watering. This practice raises the humidity around the leaves and promotes infection.
3. Buy disease-free seed and seedlings grown in disease-free nurseries. When downy mildew is discovered, rogue out and destroy infected plants. Clean up all debris including diseased leaves and fruit. Mulch around plants to reduce the amount of aerial inoculum.
4. Use resistant cultivars when available. For grape, varieties that flower and fruit later show the greatest resistance to downy mildew. Cultivars with large juicy berries are the most susceptible.
5. Use preventive fungicidal sprays. Fungicide sprays for downy mildew can be applied at 5 to 10 day intervals when humidity is high and temperature are above 50 degrees F. If the weather turns dry, fungicide applications can cease. Check manufacturer’s label for rates and crops. | 
