West Michigan tree fruit update – June 20, 2017

Much needed rainfall and cooler temperatures provide relief.

Weather and tree fruit development

Fruit development continues and all tree fruits are beginning to size with many apples now in the 22- to 27-millimeter stage. June drop continues. Fruit set is extremely variable across the general Grand Rapids, Michigan, region. It’s becoming easier to tell what is setting, but a little too early to put an accurate guess on the total crop for the area.

Some much needed rainfall came over the past weekend and that too was variable. See the table below for rainfall totals for the past seven days at Michigan State University Enviroweather stations around Grand Rapids. Cooler weather is now in place for a few days.

Total rainfall throughout Grand Rapids area from June 12 – 19, 2017, as of 5 p.m., June 19, 2017.

Enviroweather station

Rainfall (inches)









Kent City




Sparta 20m Tower


Standale / Walker


West Olive


Pest development

All primary apple scab ascospores are now fully discharged with the heavy rains over the weekend. The last spore catch was on June 14, 2017. There is primary scab present in some blocks from the long wetting period and infection in late April. In blocks with active scab, fungicide covers need to continue at full rates until leaves and fruits become a bit more toughened in mid-July.

A bit more powdery mildew can be found in susceptible apple cultivars, but overall mildew infections continue to be low. The weather last week was perfect for mildew, so continue to protect susceptible varieties as needed as long as terminal growth continues.

Codling moth trap numbers continue in varying levels and should be on the decline for first generation. We are at peak egg hatch and cover sprays continue to be very important and need to be reapplied in blocks over threshold due to the heavy rain recently. A regional biofix was set for May 15, 2017 (250 GDD50), and 530 GDD50 have been accumulated. Good residues need to be maintained for the next three weeks to get through first generation codling moth egg hatch.

Obliquebanded leafroller adults in traps are declining as expected. A regional biofix was set for June 8, 2017 (1017 GDD42), with 337 degree-days accumulated since then. High pressure blocks should begin obliquebanded leafroller sprays late this week (June 22–23) to be timed with early egg hatch. Low pressure blocks can scout for larvae and spray.

San Jose scale adult male flight has ended. Crawlers are starting to be found in known hot spots. A regional biofix was set for May 21, 2017 (318 GDD50), with 462 GDD50 since then, which also indicates crawlers should be active and targeted with cover sprays in high pressure areas.

Second generation oriental fruit moth adult flight continues to increase week-to-week. A regional biofix was set for April 28, 2017 (307 GDD45), and 810 degree-days have accumulated since. We are in between generations of susceptible larvae. Cover sprays will again be needed in the first week of July in all stone fruits and any apples with high pressure.

All stages of European red mite continue to be found. Predator mites are also present. This very hot and dry weather could push mite development, so keep an eye on mites. Threshold for June is 2.5 mites per leaf.

Various species of aphids can be found in all tree fruits. Green apple aphids continue to build in some blocks. More reports of woolly apple aphids are coming in this week—they are creating colonies around pruning cuts. Monitor for all aphid species in all tree fruits as well as the beneficials that attack them.

Dogwood borer adult flight is beginning. Monitor burr knots for activity and traps for population potential and peak flight. Trunk sprays go on with peak adult flight, typically the first week of July.

Various chafer beetles are active. Rose chafers continue in peach blocks with sandy soils. European chafers are starting evening activity in turf, which usually means Japanese beetles are a week or two away.

Spotted wing Drosophila (SWD) flight continues to be reported and is starting to make that jump forward to indicate cover sprays are needed in crops just coming into ripeness. This could be a high pressure year for SWD, as they have never been trapped this early in Michigan. Don’t delay cover sprays.

Brown marmorated stink bug overwintering adults can be found and newly laid eggs are hatching. They are not attracted to tree fruits as a food source. Monitor for adults and nymphs. Management in tree fruits will target adults in summer when fruits near ripening and become attractive as a food source.

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