What do downy mildew forecasts mean?
The Disease Forecast Center uses information about the location of sources of inoculum (ie, downy mildew spores from an existing field outbreak) along with predicted air movement from the source into other regions (the trajectory of spore transport), predicted survival of the spores (cloud cover or sun) and predicted rain (‘washout’ or deposition of spores) to assess the risk that live spores will reach a certain area and that conditions for infection of crops will be favorable. Sunny conditions kill spores, while cloudy conditions allow them to survive. Rain causes them to ‘washout’ and be deposited in an area. These factors are all combined to determine a risk rating. The risk for a certain area may be ‘low’, ‘weakly moderate’, ‘strongly moderate’, or ‘high’. This forecast site is updated twice weekly. —Bess Dicklow and Ruth Hazzard.
