Model A: Timed Interval Spraying
This model is used in regions where late blight continues to be a threat yet does not occur every year.
Model A uses a daily disease severity scale from 0 to 7. These values, called SPUD values, rate each day according to the favourability of weather conditions towards the development of disease. Growers are advised to apply an initial spray when 150 SPUD values have accumulated after crop emergence. Subsequent fungicide applications are applied after accumulating an additional 50 SPUD values since the last application.
Model B: Dynamic Dosage
This model is used in regions where late blight is a continuing threat, with local outbreaks occurring every year.
Model B, the Dynamic Dosage model, allows growers to continue with their regular spray intervals of 7-10 days, but allows for better decision making when it comes to choosing the type of fungicide needed and the proper label rate to apply. Most potato fungicide labels and provincial crop protection publications provide a range of chemical rates for early and late blight. Model B gives growers advice about when to use the lower or higher recommended rates of the protectant fungicides available, and when to switch to a late blight targeted fungicide based on weather conditions over the past seven days.