Northwest Michigan fruit update – Aug. 4, 2020
Cherry harvest is nearly complete and apples are sizing nicely.
The weather has turned cool and damp for the past two days, and for some it has been a welcome change. This change in temperatures follows a dry, warm and pleasant stretch of weather that has been excellent for harvest. For the past week, daytime temperatures have been in the mid-70s and nighttime temperatures dropped to the low 60s. Most Michigan State University Enviroweather stations reported some amounts of rainfall on Monday, Aug. 3, and the rainfall amounts were variable, but humidity levels have been pretty high across the region.
Temperatures are expected to rise again after today, Tuesday, Aug. 4. Some forecasts are predicting daytime temperatures up into the high 80s through the weekend. Thus far, we have accumulated 2,256 growing degree days (GDD) base 42 and 1,508 GDD base 50. We are almost spot on with our long-term averages: 2,284 GDD base 42 and 1,468 GDD base 50.
Most growers have finished cherry harvest for the season, and fruit quality remained high throughout the harvest period. Some growers are still harvesting tart cherries but anticipate finishing up this week. Some growers were surprised to see a bigger crop than anticipated while other growers finished up quickly due to a smaller crop.
Apples are sizing nicely, and some varieties are starting to show color. Some growers are hand thinning at this time. However, most growers report excellent thinning this season, either by natural causes or thinning programs. Growers are anticipating a good apple harvest this season.
Apple pest update
We found one apple maggot on our traps this week for a total of two flies so far this season; the first apple maggot was detected in our trap line last week. We received reports that apple maggot numbers are also low in commercial blocks in the area. Peak emergence typically occurs in early to mid-August, between 1,400-1,700 GDD, but activity is highly site-specific and related to good soil moisture conditions.
We observed a decline in codling moth catches in our traps with just one moth per trap; low catches could be related to recent cooler conditions slowing flight activity. As indicated last week, second generation moths are likely flying at this time. Using July 28 as a biofix for second generation flight at the Northwest Michigan Horticulture Research Center, egg hatch will begin toward the end of this week. However, the best way to estimate moth activity and when egg hatch will occur is to monitor on farm. Lastly, a good resistance management practice is to use a material with a different mode of action for the second generation than was used for the first.
Mite populations continue to be high and we have even observed some predatory mites this season. While it is good to see these natural enemies, most orchards are not supporting high enough predator populations to keep pest mites in check. Cooler weather will have helped to slow mite development, but warmer weather ahead will be once again favorable for development. Continue to monitor populations, especially after applying miticides to evaluate efficacy. Keep in mind that all life stages are present and not all miticides provide efficacy against all of the mite life stages (i.e., eggs and motiles).
San Jose scale male flight is ongoing, and we have not observed a second wave of crawlers at this time. However, emergence should be beginning now.