West Michigan tree fruit update – Aug. 8, 2017
Insects don’t take a summer vacation – don’t let your guard down.
Crop stage and horticulture information
Harvest of mid-season peaches continues. Peaches continue to size well and quality has been excellent. Apples too are sizing well and are generally between 2.25 and 2.75 inches in size.
Rainfall has been variable and minimal in the last month. We are in a water deficit in much of the general Grand Rapids, Michigan, area with irrigation systems running to make up for moisture. Growing degree-days (GDD) continue to track about four to eight days ahead of normal averages for the first week of August.
Our 2017 predicted apple harvest dates seem to be right on target when looking at the early varieties. The 2017 predicted harvest dates for upcoming varieties in the Grand Rapids are: Paulared—Aug. 19; Gingergold—Aug. 21; Gala—Sept. 5.
Pristine were mature on the Ridge around Aug. 1. Normal harvest date for Pristine is Aug. 5, so they are coming in about four to five days ahead of normal. We use Pristine as an indicator of predicted harvest dates.
Paulared apples are large to very large. The starch clearing on Aug. 1 was 15 percent (starch index of 2) on the apples with moldy core/watercore. Probably seven to 10 days to go yet to harvest.
Gingergold apples have zero percent starch clearing (starch index of 1). They are still a week or so off, however, fruits with moldy core are turning yellow now. Keep an eye on them.
Codling moth adults in traps are declined as flight of second generation is ending. It is estimated that second generation eggs are 25 to 35 percent hatched and management is necessary in blocks over threshold. A second generation regional biofix was set for July 19 (1,307 GDD50) with 368 GDDs accumulated since then, indicating second generation codling moth needs to be managed for at this time in blocks over threshold.
The Michigan State University trap line is catching all stages of brown marmorated stink bugs in various traps. Numbers are higher than 2016, but still overall quite low compared to other regions of the U.S. with very high pressure and damage. As you are managing for codling moth, this is a good time to add something in the tank for early brown marmorated stink bug management covering the whole block. Follow-up sprays in the next weeks until harvest could most likely target the borders where pressure is still low. High pressure blocks will need whole block covers about every two weeks. There is a great publication from the Michigan State University Extension fruit team for all things brown marmorated stink bug, “Managing Brown Marmorated Stink Bug in Michigan Orchards.”
Apple maggot adults continue to be caught in traps. Numbers still seem low, most likely due to lack of rainfall. There has been a marked increase in apple maggot damaged fruits in the general Grand Rapids area over the last two or three years and all blocks should be trapping for it. Traps should be in place in known hot spots and along orchard edges near wooded areas with alternate hosts present. You only know what’s happening with apple maggot if you are trapping for it correctly. Red spheres with essence lures are the best for apple maggot and reapply tanglefoot as needed.
Adult flight continues for the summer generation of obliquebanded leafroller and numbers are all over the board. It is estimated we are nearing 50 percent egg hatch. Small larvae will become easier to find in about a week, just in time for Paulared harvest. A second generation regional biofix was set for July 19 (2,120 GDD42) with 520 GDD base 42 accumulated since then. Continue to monitor for visible larvae and manage accordingly.
All stages of European red mite can now be found. Predators are also more readily found. In the last two to three weeks, red mites seemed to have jumped in activity and some bronzing can now be seen. Some blocks have a high number of eggs present, so populations will continue to build. Continue to monitor red mite and beneficial mite populations. Threshold for August is 7.5 mites per leaf. At this time of the growing season, adults will begin to lay eggs in the calyx end of apples and are not easily washed off fruits post-harvest. For blocks with decent fruit set, management should be considered if mites are over threshold.
San Jose scale males are flying and no crawlers have been reported. A second generation regional biofix was set for July 27 with 191 GDD base 50 since. Crawlers could begin to show up in the next week and cover sprays should be considered in blocks with San Jose scale damage in 2016 to target crawlers in the next seven days.
We should be right in between second and third generation oriental fruit moth activity, and cover sprays are not as critical where pressure is low. A regional biofix was set for April 28 (307 GDD45) with 1,950 GDD base 45 accumulated since that date. This a good time to change out lures if needed to accurately catch third generation. If you are under mating disruption for codling moth in apples, consider adding an oriental fruit moth trap to your disrupted blocks; third generation oriental fruit moth can sting apples if not managed.
Japanese beetle continue to be found and seem to be declining a bit. Continue to monitor and manage as needed.
Most have discontinued trapping as spotted wing Drosophila is now uniformly present in high numbers across the state. Consider cover sprays in late peach blocks. This pest is not a problem in apples.
For summer diseases, second applications of fungicides should be considered if you haven’t added them in already. It’s been an overall drier summer and pressure for summer disease in apples is much lower. We are very similar to 2016 so far. In 2016, the rains late in the season gave us tremendous pressure for sooty blotch and flyspeck at a time when fungicides had definitely run out.
Please consider using the model for summer diseases on the MSU Enviroweather website for the station nearest you. You can put in your fungicide application date and it will calculate the need for re-application.