Grand Rapids, Mich., area tree fruit regional report – May 14, 2013

Freezing temperatures early in the week caused little overall damage to tree fruits in west Michigan.

Growth stage update

Tree development slowed a bit with the weekend’s cooler weather. Overnight lows Sunday into Monday night (May 12-13) were a little lower than expected in some locations, probably due to low dew points, no cloud cover and no winds. At this time, there is a full crop potential for all tree fruits with some flower damage, but probably not enough to have a significant effect on the overall crop.

Apple scab update

The weekend rains were varied across the west Michigan area. To the north in Hart, Mich., and Ludington, Mich., it was one long, moderate infection period that started in the night on May 9 or 10, depending on the Enviro-weather station site. For the stations on the Ridge and in Belding, Mich., there were two distinct wetting periods over the weekend and according to data from the Sparta, Belding and Fremont Enviro-weather stations, the first wave of rain that began on May 10 after midnight resulted in a light apple scab infection period, but for Kent City’s Enviro-weather data it indicates it was one hour short of a light infection period – pretty close to not say you should have had a cover on.

I caught a total of 443 spores on average for the May 10 rain. Then, more rain moved in on May 11 in the afternoon, giving Belding, Sparta, Kent City and Fremont another eight to 15 hours of wetting at very low temperatures near 40 degrees. We’d need 30-plus hours of wetting at these low temperatures to get a light infection, so there was no additional infection from the May 11 rains. I did catch the highest level of spores with the second wave of weekend rain on May 11, an average of 1,219 spores per rod.

As of today, May 14, growing degree days base 32 indicate we are probably about 45 to 50 percent spore maturity right now, so Michigan State University Extension expects some very high spore release numbers with any rains over the next two weeks, so be sure you are keeping adequate fungicide covers on; this is not the time to stretch fungicides out too far.

Powdery mildew

It’s always a good idea to add something in the tank from pink to petal fall for powdery mildew in apples and probably even more so this year with higher levels of inoculum coming into this season.

Fire blight

The cold, wet weather last weekend posed no threat for blossom blight, but the risk goes back up later in the week with warmer weather in the forecast. Fire blight bacteria will build again in blossoms from Wednesday (May 15) on and any rain we do get on open, viable bloom on fire blight-susceptible cultivars will be at risk. There is also the risk for thunderstorms this week with warmer temperatures, so keep blossom blight on your radar for the next seven days.

Brown rot

Brown rot sprays in stone fruits should continue to be maintained until we get to shuck split in peaches, plums and cherries to help prevent brown rot from getting started.

Apogee use

Many of you already use Apogee on apples routinely in your tree management programs and with this potential for blossom blight this year, it will surely be important to apply Apogee this year. The ideal timing for Apogee is when the new shoots are 3 inches in length or at the beginning of petal fall of the king bloom, which is really just about any time over the next seven days.

Thinning meeting

There will be a thinning meeting this Thursday, May 16, from 8:30 to 10 a.m. Our host will be Chris Kropf and we will meet at his Hart, Mich., farm located at 12301 Hart Road, Greenville, MI 48838 (view map). We will meet by the boxes near the entrance off Hart Road.

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