Penn State Extension Full Article Here May 3, 2018
Severe fire blight and apple scab disease conditions are predicted for May 3–5, 2018! Protection is absolutely necessary!
The weather forecast appears to be coming to fruition. We will have optimum conditions for severe infections periods for both fire blight and apple scab from May 3 through May 5.
Fire Blight Management
For fire blight, protecting open blossoms with streptomycin is necessary. With the warm temperatures, any bacteria on the stigma will be replicating to very high numbers. The streptomycin spray will kill any bacteria present so none will be available to wash into the nectaries when the rain occurs.
In addition, combining streptomycin with a plant immune system inducer, such as Actigard (2 oz/A), Vacciplant (20 oz/A), or Regalia (2 qt/A), is an option to consider since this will give you a bit of extra protection through the weekend and early part of next week. We have observed Regalia cause brown speckling on the flower petals; however, this does not seem to interfere with pollination.
Apple Scab Management
For apple scab, we are in the middle of the peak for the maximum number of available spores to cause infection when a wetting event occurs. Only 6 hours of leaf wetness is necessary for infection to occur since our average temperature right now is in the ideal range. Protecting trees before the wetting event is encouraged. As a reminder, fungicides with the FRAC Group 7 mode of action are encouraged during this period.
These are extreme conditions we are experiencing. Growers must stay on high alert!