Grand Rapids, Mich., area tree fruit regional report – June 4, 2013
Primary apple scab is not over just yet for west central growers.
Growth stage update
Apples are 12 to 16 millimeters in general and the apple thinning window is quickly closing on the Ridge. Temperatures this week are not especially favorable (warm) for thinners to really work well.
No blossom blight symptoms have been reported on the Ridge and it is likely that if you had any blossom blight infections from the high risk situations during bloom, they would be showing up by now. This is good time to carefully scout blocks for blossom blight.
Apple scab update
A dry start to the spring apple scab season has ended with an unusually wetter than normal situation. There have been several wetting periods in the last two weeks with many being scab infections. There is quite a bit of variability in wetting periods at the various Enviro-weather stations around west Michigan.
There is some light amount of primary scab showing up in a few commercial blocks and it’s most likely from the infection on May 10, which was not the most significant infection of the season. The remaining infections that occurred after the middle of May should start to express themselves over the course of this week. Hopefully, growers do not see lesions, but as we are nearing the end of primary scab spore discharge, it is a good time to do some very careful scouting for apple scab to be sure you are clean before you reduce primary scab fungicide rates for the season. We should be very near or past 100 percent ascospore maturity for the Ridge and much of west Michigan, but we do need at least one or two more nice daytime rains to release any remaining mature spores not yet discharged.
There is some powdery mildew showing up in apples, but it is less than expected compared to how bad it is in non-sprayed trees at this time.