Grand Rapids area tree fruit update – April 14, 2020
Cooler weather will stick around for awhile in Michigan’s Grand Rapids area.
Then winter of 2019-2020 was quite mild with very limited snowfall through the season. The total precipitation for the winter was more than adequate, but it came in the form of rain more so than snow.
Degree day totals for the general west Michigan area are slightly ahead of normal averages, and ahead of this time in 2019. The Michigan State University Sparta Enviroweather station has accumulated 149 degree days base 42, which is two days ahead the average for Jan. 1 to April 13. Degree days base 50 at Sparta are 45, which is three days behind normal from Jan. 1.
Colder than normal weather is on tap for the next several days and advective freeze events are likely. Wind machines will not be of use in an advective freeze event, and you might get a degree or two out of microspinklers until they freeze up. Hopefully the wind will hold up and some clouds will hang on to lessen cold. Apples are mostly in the 0.5-inch stage with a critical minimum temperature of 23 degrees Fahrenheit for 10% flower bud kill and a temperature of 15 F for 90% kill. If you have some apples in the tight cluster stage, the temperature is 27 F for 10% kill and 21 F for 90% kill. I think Thursday morning, April 16, will be dicey.
A bit of tree planting has started and with soils being on the drier side right now; that’s a good job to get done if you can. Check out this article for pointers on best practices for apple tree planting.
I catch a few apple scab spores with each rain event, but they seem to be slower this year in their development. With the lack of long-term snow cover and milder conditions over the winter months, this does not surprise me. It's likely we could expect a slower development and lower early discharge levels of primary apple scab spores. This is a good way to start the spray season, but don't be fooled—the spores will be there in high numbers like they usually are between 0.5-inch green and first cover. All the Grand Rapids area weather stations have logged at least one apple scab infection so far this season on April 7, 2020.