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Apple Scab and Powdery Mildew Updates - Watch for the First Scab Lesions this Week

Posted: April 13, 2012

Apple scab lesions should be expected this week on trees that were not adequately protected March 20th to 25th. Any infections could lead to a severe secondary infection on April 17th, given the current weather forecast.
Dr. Noemi Halbrendt, Penn State Fruit Research and Extension Center Plant Pathology Associate

During the first twilight meeting of the season (April 12th), Dr. Keith Yoder, Virginia Tech Professor of Plant Pathology, spoke about the disease situation.  Summarizing the scab status to date, he said that the first ascospores were trapped on March 19th, and that scab infections occurred on March 20th to 25th and March 31st to April 1st.  During the latter infection periods, there were fewer ascospores than on the earlier dates, but the numbers were still significant.  Proper and thorough spray coverage at this time of the year is critical!

We tend to pay more attention to apple scab, but powdery mildew spores were likely available on infected emerging buds by March 23rd.  Since March 20th, mildew has outscored scab in infection days (10 vs 8), with "dry weather mildew infections" on March 25th to 27th, 29th and April 3rd to 8th.