West Michigan tree fruit update – April 18, 2017
Tree fruits are responding nicely to warmer weather.
The warmer weather has helped to move tree development at an even pace, with no explosion of growth for the most part. The range of growth in apples seems more significant this year—early developing apple varieties (Ida Red, Gingergold, Zestar) are in the tight cluster stage, while late developing varieties (Rome, Spy, etc) are barely at green tip.
Early developing sweet cherry varieties and sites have a few open blooms. Peaches are right behind the sweet cherries. All flowers of all tree species appear to be very healthy this season, with little to no winter injury.
Cooler weather is on tap for the future, so make sure your frost fans are in working order. The critical minimum temperatures for tree fruits should be around 25 degrees Fahrenheit right now for most species and varieties.
There have been several rain events in the past two weeks, with only the April 10 wetting event resulting in the first apple scab infection of the season, having enough green tissue present to be a risk. Spore release numbers started out in the single digits and crept up to over 100 with each daytime rain event since then. We are at the very beginning of the primary apple scab season, but green tissue is very susceptible to infections and needs to be well-covered.
The forecast for Wednesday night into Thursday (April 19-20) is for temperatures to average in the low 50s, which, according to the Mills Table modified by Jones, would require 12 to 15 hours of wetting in order to get an infection. With the various forecasts as they are right now, it seems likely that we could at least have a light infection, and good fungicide covers are needed ahead of this rain event.
It’s a bit too early to be concerned about powdery mildew in apples—for most blocks, you can wait to add mildewcides closer to the bloom stage. For any blocks with a history of powdery mildew, you might want to begin adding mildewcides a bit earlier at the pink stage or even at tight cluster stage.
Regarding apple insects, there is nothing much to be concerned about at this time. Spotted tentiform leafminers are flying in very low numbers; a few redbanded leafrollers are present, but of little concern; and green fruitworm adults are flying.
If you had high levels of San Jose scale on fruit at harvest in 2016, Michigan State University Extension suggests tightening up your management program for this pest. There are several chemistries that can be used in the pre-bloom apple period to help reduce the eventual numbers of crawlers. Every year for the past five or six years, I see more and more scale on fruits in the bins.