Will the hot weather reduce powdery mildew pressure?
The 90 degree forecast made me reflect on Powdery Mildew risk indexes used in the West, but rarely applicable here in the Finger Lakes – because it doesn’t often get that hot. Well, it’s that hot, so is it going to help us out with powdery mildew pressure? I looked up UC-Davis pathologist Doug Gubler’s PM model to refresh my memory. Basically this model uses temperature to assign a ‘risk rating’. ‘High risk’ is defined as hours with temperatures between 70-85 degrees F – the optimum for PM growth. At temperatures above 90, the model shows ‘intermediate’ risk – at 90, PM growth essentially stops – and above 95 the model lowers the risk rating (because hot temperatures kill the PM fungus).
The model then recommends longer spray intervals (up to 14 d for sulfur) for ‘low risk’ conditions, or shorter ones (7 d for sulfur) for ‘high risk’.
we are 12 to 14 days ahead of LT averages...