West central Michigan tree fruit regional report – August 11, 2015

Latest rainfall totals were highly variable.

The last front that moved across Michigan brought highly variable rainfall totals to west Michigan. The Michigan State University Sparta Enviro-weather station recorded just under 2 inches of rain with other nearby stations reporting no rain at all. Some growers reported over 3.5 inches in their rain gauges. Growing degree day (GDD) totals in general are running about three to four days ahead of normal averages.

Peach harvest is going well with good quality and size. Early summer apple varieties are being harvested in light amounts. Growers are likely to start with Paula Reds in about a week and Gingergold soon after.

Tree fruit Insects

Codling moth second generation adult flight has been reported in several blocks over the last seven to 10 days. A regional generation two biofix was set for Aug. 2, or 1,550 GDD50 from Jan. 1. GDD since biofix is 175. In high pressure blocks, cover sprays should go on for second generation codling moths very soon. In moderate pressure blocks, time sprays for 250 GDD50, which should be by the end of this week. In low pressure blocks or those with disruption, time for 325 to 350 GDD50 post-biofix, which should be sometime early next week.

European red mites are beginning to build in some blocks. Continue to carefully monitor mite populations and the beneficials that attack them. Threshold is 10 mites per leaf for August. There are quite a few beneficials in mite populations – if you see one mite predator per leaf, wait a week and count again before applying any miticides.

Obliquebanded leafroller adult flight should begin to increase, but it seems to be delayed in getting started. A regional biofix was set for June 12, or 1,036 GDD42). GDD since biofix is 1,594. Continue monitoring for summer generation adult flight. Lures should be changed in traps for the best monitoring.

San Jose scale second generation adult male flight is well underway and a few crawlers are starting to be reported. This is the generation that will settle right on apple fruits as well as limbs. The window to manage is right now. Continue to monitor activity.

Oriental fruit moth second generation adults and egg hatch should be at an end. Adult numbers are increasing slightly as third generation flight begins. We are at a break between oriental fruit moth generations right now and cover sprays are less important. This is a good time to change out lures if needed to be sure you are monitoring for third generation adequately. Having an oriental fruit moth trap in apples under mating disruption is highly recommended by Michigan State University Extension and it’s not too late to add one to your trapline.

A regional biofix was set for May 6, or 256 GDD45. GDD since biofix is 2,013. Expect third generation oriental fruit moth egg hatch to reach 10 percent about a week from now, Aug. 18-20 for the general Grand Rapids, Michigan, area, with peak egg hatch around Sept. 1. This generation can catch the end of late-season peaches as well as infect apples in blocks with high adult numbers, estimated to be more than 40 to 50 moths per trap per week.

Adult maggot trapping continues, but overall in mostly low numbers. There are some hot spots and all blocks need to continue being monitored for this late-season pest. The recent heavy rain that some areas had could push them from overwintering sites in the soil – watch traps closely for a spike in numbers.

Brown marmorated stinkbug adults have not been trapped in west Michigan, but there has been some suspect damage to peaches.

Japanese beetles numbers are declining in tree fruits. Continue to monitor for another two weeks.

Tree fruit diseases

In regards to summer diseases in apples, growers are encouraged to follow the summer disease model at the MSU Enviro-weather station nearest your location to determine when follow up fungicide applications are needed for sooty blotch and fly speck. With the recent variable heavy rainfall, you might need to recover for a final time prior to harvest.

Silver leaf in apples can be seen more abundantly this summer than I can ever remember. It is caused by a slow growing fungus that likely entered trees that were injured by the cold weather from the 2013-14 winter. It got started during the 2014 growing season and now, in 2015, we are seeing the symptoms. This is just one aspect of the cold winter damage we are likely to continue seeing over the next few years. Typically, this disease causes a slow decline in tree vigor and yield, and is not always expressed every year. However, given the tissue damage from cold injury and the presence of the silver leaf fungus, and likely other slow-growing fungi as well, I expect these trees to decline more quickly than typical to an early death in the near future. It would be best to remove trees if they are showing signs of silver leaf and winter injury. Since this is a fungal disease, please remove it entirely from the orchard and burn it to prevent further infection of remaining trees.

This season was tough to stay on top of apple scab. If you are fighting scab, be sure to keep fungicide covers on to prevent further spread. Once we move past the hot, dry weather of summer, fruits and leaves again become more susceptible and fungicide covers are needed to prevent apple scab infections from continuing.


Pay close attention to the pre-harvest intervals (PHI) for any cover spray you are considering. The 2015 predicted apple harvest dates will be similar to 2014 and maybe even a day or two ahead of that. 

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