West central Michigan tree fruit update – May 28, 2019

David Jones, Michigan State University Extension - May 28, 2019

Apples are approaching the end of bloom. Tart cherries are at petal fall, peaches and sweet cherries are in the shuck.

Weather

Conditions continue to be cool and wet throughout the region. Heavy rains in the tail end of last week brought more than 2 inches of rain in some spots, forcing many growers to re-cover orchards that they had been in just three to four days before as more rains rolled in. Repeated light rains nearly every day for two weeks have presented some frustration to growers trying to sustain regular fungicide coverage and consistent field work.

Station	GDD base 42 F current	GDD base 45 F current	GDD base 50 F current
Benona / Shelby	435	327	191
Elbridge / Hart	465	350	203
Hart	452	339	194
Ludington	427	316	176
Mears	475	356	206
New Era	520	397	239
Shelby - East	475	355	204

We are still well behind five-year averages for growing degree day (GDD) accumulation. This has been easy to observe this year even without looking at data, as tree fruit development has been extremely late. Insect activity has also been extremely minimal so far this year, although activity of several prominent pests will likely pick up in the next week as tree fruit moves away from bloom.

Year	GDD base 42 F	GDD base 45 F	GDD base 50 F
2019	452	339	194
2018	603	487	328
2017	660	505	305
2016	654	516	330
2015	614	487	318
2014	490	378	227
Average of 5 years	604.3	474.5	301.6

Crops

Apples are approaching either full bloom or petal fall, depending on site and variety. Pollinator activity has been decent despite the cooler weather—a late spring has made hives desperate, so bees have been observed working flowers in conditions that have been windier and cooler than we would typically expect to see activity. Codling moth will likely start showing up towards the end of the week as some blocks move into petal fall. We have had either one or two apple scab infections in the past seven days, depending on location. Rains forecasted to arrive on Saturday, June 1, are forecasted to trigger another infection event.

Growers were gearing up for a bad week for fire blight this time last week, as they looked at forecasts of warm, wet weather. However, weather ended up being cooler than forecasted, resulting in EIPs that rarely crept above 70 for most of the week. EIPs at 70 or higher still constitute sufficient risk to warrant an application on high value fresh market varieties, particularly on susceptible varieties such as Gala and Fuji, so growers needed to be out over the weekend protecting blossoms in these orchards. Another cool week ahead will likely keep fire blight risk low, but keep an eye on the Michigan State University Enviroweather fire blight model each day to assess risk.

Thinning time is not far off, and if current weather patterns are sustained, it is looking likely that apple tree carbohydrate stress will be low this year during thinning. This will present some challenges as many area growers prefer to get their thinning done all at one go with an application timed around the 10-millimeter stage. This could shape up to be a season where getting started with thinning early will be important, as one-shot thinning during a low stress year can yield particularly unpredictable results.

Tart cherries are at petal fall. Bloom was extremely rapid this year. Growers had a fungicide cover out last week ahead of the rains to protect against cherry leaf spot, but rain accumulations over 2 inches in the second half of the week forced growers to re-cover orchards quickly ahead of the next round of rains over the weekend. It has been an eventful week for cherry leaf spot infections—we have seen as many as three separate infections events, depending on location. Early leaf spot infections on bract leaves should now be visible in affected blocks.

Sweet cherries are at petal fall or in the shuck. The crop generally looks good, although growers have reported some scattered damage from some cold nights that we experienced at the tight cluster stage this year. Keep an eye on plum curculio in the next few days as sweet cherries emerge from the shuck, particularly if weather warms up. Activity from this pest is not far off.

Peaches are at petal fall or in the shuck. The peach crop looks good this season; expect a full crop that will require some thinning. First generation of oriental fruit moth is in flight, with an estimated regional biofix of May 20. Tarnished plant bug and oriental fruit moth need to be managed at petal fall; avoid pyrethroid insecticides when controlling oriental fruit moth in light of recent work demonstrating pyrethroid resistance in local oriental fruit moth populations. San Jose scale flight has not started, but keep an eye on San Jose scale activity in coming weeks to target applications in blocks with a history. Peaches in west central Michigan have been an easy crop to find San Jose scale in recently.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).