Summary of last week's infection events, May 15-19.

At our AREC in Winchester we recorded a very long apple scab and rust infection period May 15-19, with 89 hr of almost continuous wetting at an average of 63° with 5.2 in. rain. We had observed scab lesions prior to this infection event, so potentially this was a very serious secondary infection where there was little fungicide protection to cover the event through five inches of rainfall. Some of the wetting occurred at temperatures near 70° and was favorable for moldy core infection and the start of summer disease activity. 

As a follow-up to this extreme infection period, a suggestion is to apply combinations fungicides with protectant activity and two classes of fungicides to offset the potential for resistance in apple scab; also include an SI fungicide for after-infection activity for cedar-apple rust. A second follow-up application should include another class of activity for scab plus a protectant fungicide.

This weather was also favorable for cherry leaf spot and peach scab, which will remain active for the next month. At our AREC we have had 22 apple powdery mildew infection days since Apr 10. With the long wetting last week, mildew activity was somewhat reduced, but it will be quite active with susceptible shoot growth this week

Other areas in Virginia also experienced long continuous or split wetting periods with amounts of rainfall ranging from two - five inches. We are near the transition from early season to summer disease control, but all areas should be concerned about remaining apple scab, as well as moldy core and early summer disease activity, especially bitter rot. The timing of this event might have also left an opening in protection against for Brooks fruit spot.