Disease update: recent and ongoing scab and rust activity

We have had a lot of apple scab and rust activity this past week, and more on the way. At our AREC we recorded scab and rust infection periods May 10-11 (15 hr wet at 62° with 0.05 in. rain), and May 14-15 (13 hr wet at 66° with 1.11 in. rain). As of the morning of May 16 another infection period is in progress and much rain and wetting is in the forecast for the next three days. We observed scab lesions, probably from infection periods Apr 15-16 or Apr 24-25, on leaves at the base of unprotected shoots. Cedar-apple rust galls are still actively producing spores. 

This weather is also favorable for cherry leaf spot and peach scab, which will remains active for the next month or so.

As indicated in the update May 14, these wetting events at temperatures in the 60s constitute fire blight infection events wherever susceptible flowers are present. Another threat is possible secondary shoot blight with bacteria spreading from blossom blight symptoms now appearing from infections May 5 and 7, and driven by a series of thunderstorms with some scattered hail.

At our AREC we have had 21 apple powdery mildew infection days since Apr 10.