Grand Rapids area tree fruit update – August 23, 2022
Conditions this week were mostly clear and near or slightly warmer than normal.
Weather and phenology update
Conditions in the Grand Rapids, Michigan, area this week were mostly clear and near or slightly warmer than normal. Temperatures were in the upper 70s to 80 degrees Fahrenheit all week, with overnight lows in the upper 50s to 60. As of Aug. 22, the Michigan State University Sparta Enviroweather station has accumulated 3008.7 degree days base 42 F (DD42). This is slightly above average, which is 2862.2 DD42, and approximately five days ahead of normal.
Rainfall over the past week was variable. On Tuesday, Aug. 16, most weather stations recorded several tenths of an inch. On Saturday, accumulation varied between less than 0.1 inch and greater than 1 inch, with little rainfall in the Sparta area and greater rainfall in Standale, Belding and Clarksville areas. Soil moisture in most of the Grand Rapids area is near normal, and most areas not experiencing drought conditions, according to the U.S. Drought Monitor.
Expect fair, dry conditions Tuesday and Wednesday, Aug. 23 and 24, with a storm system moving into the area Wednesday evening. Rainfall accumulation Wednesday night and most of Thursday will likely be less than 0.25 inch. Cool, dry conditions are expected Friday and Saturday. Another chance of rain is expected Sunday and Monday, with more accumulation. Medium range forecasts indicate slightly warmer and wetter conditions than normal.
Tree fruit is continuing to put on size and color. Apples are just beginning harvest in early varieties such as Zestar, Ginger Gold, Paula Red, as well as Premier Honeycrisp and Wildfire Gala. Harvest of standard strains of Honeycrisp and gala are expected in two to three weeks.
Tree fruit diseases
Summer disease management in apples should be considered in areas where the Michigan State University Enviroweather model indicates adequate wetting hours for disease expression. The wetting hour totals vary greatly from station to station this year—be sure to check the summer disease model on Enviroweather for the weather station nearest you for guidance. If you want to read about how to use this model, see About Enviroweather's Sooty Blotch and Flyspeck Progress.
Fruit rots could be enhanced with higher rainfall that washes away fungicide cover sprays. Temperatures and relative humidity levels have been moderate to average but are still favorable for fruit rots when fungicide residues are lacking. High heat and high humidity greatly favor fruit rots.
Tree fruit insects
A second generation biofix for codling moth was set for July 19 (1330 DD50). We’ve accumulated 675 degree days base 50 since. This indicates egg hatch if occurring and cover sprays are critical to protect fruit from infestation. I expect second generation to be a concern in blocks over threshold at least until Labor Day, Sept. 5. Don’t get to stretched out on your cover sprays between now and Labor Day.
A Grand Rapids regional biofix for obliquebanded leafroller was set for June 14(1076 DD42) with 1958 degree days accumulated since, indicating second generation larvae should be visible at this time. Some fruit damage can be found in higher pressure blocks.
A Grand Rapids regional biofix for oriental fruit moth was set for May 12 (312 DD45) with 2301 degree days base 45 accumulated since. This is the proper timing for the third generation eggs to be at an early hatch stage and cover sprays are again critical if pressure is high. This third generation can sometimes be an issue in apples as the cover sprays for codling moth wane, and oriental fruit moth builds unexpectedly.
Woolly apple aphids are still too easy to find in just about every block you look in. I see good control in blocks where growers slowed down and used more water than they like to, but coverage is key with managing this pest.
A regional biofix for San Jose scale was set for the general Grand Rapids for May 20 (288 DD51) with 1657 degree days accumulated since the regional biofix. Second generation crawlers are present and should be at, or just past, peak emergence. Second generation can settle on fruits, making them unmarketable. If you do see San Jose scale on fruits at harvest, make a note of locations and treat next spring accordingly.
All stages of European red mite and twospotted spider mites are present. While recent heavy rains did help to wash some adults away, high pressure blocks will see a quick rebound with newly hatching eggs. Summer miticides should be considered in blocks over the August threshold of 15 mites per leaf. For varieties that have 30 days to go until harvest, management should be considered this year. Most blocks have a good fruit set, even heavy in some blocks. You will need all the carbohydrates you can get to finish this crop well and mites can severely curb the carbs when they are in high numbers.
Apple maggot adult emergence continues and seems to be declining as expected, but they are still present and need to be managed where traps are still catching adults.
Brown marmorated stink bug has been not very present in tree fruits this season. There are hot spots, of course, but this pest hasn’t been as prevalent as we expected it to be. Keep an eye out in apples near other brown marmorated stink bug host plants, such as soybeans. In the past, we sometimes see brown marmorated stink bug move to orchards when the beans begin to die back.
Finally, as we approach harvest dates for apples, keep in mind preharvest intervals for all spray applications. Please refer to the product label or guidelines from your end buyers and processors. There are several tables in the back of Michigan State University Extension bulletin E154, Michigan Fruit Management Guide. Look for the Days Between Final Spray and Harvest tables on pages 322 to 327.
More information and reports on normal weather conditions and departures from normal can be found on the NOAA Climate Prediction Center website, NOAA U.S. Climate Normals website, NOAA Climate Normals Quick Access Page (which may be searched by region) and Midwest Regional Climate Center website.