MSU Extension

All tree fruit crops in the Grand Rapids, Michigan, area are starting to undergo natural June drop. In apples, some check trees are dropping nearly as much as the chemical-thinned trees, but ending up with a very nice fruit set overall. Tart cherries are showing some signs of poor pollination with fruit drop occurring last week.

Tree fruit diseases

There have been some very light nighttime rains with no apple scab spore release, and finally on Monday, June 22, we had a very heavy daytime rain. There were no spores with the rain, so primary scab is over for the Ridge. It is most likely also over for Fremont, Michigan, as well. Hart and Ludington, Michigan, growing degree days (GDD) are slightly behind the Ridge and might require additional rains for all spores to be released.

Please scout carefully for apple scab. I am seeing more than I would like to. Blocks with apple scab where your spray program was good should be tested for fungicide resistance. Please let me know if this is your situation and we can arrange for samples from the Grand Rapids, Michigan, area. You can contact me at irisha@msu.edu.

Overall, fire blight has been very low in the Grand Rapids, Michigan, area this year and this is good when stormy conditions are in the forecast – it reduces potential for trauma blight, but does not eliminate it as long as shoots are still actively growing. The storms that moved across the area Monday afternoon brought heavy rain and some wind, but no reported hail as of 6 p.m.

Powdery mildew continues to spread in some blocks. It will continue to spread with no management and as long as shoots are actively growing.

Regarding summer diseases in apples, we are approaching the timing when fungicides for sooty blotch and fly speck need to be added in to prevent these diseases on apple fruits. There is an excellent decision-making model for summer diseases on Michigan State University’s Enviro-weather website.

Tree fruit insects

Codling moth adult flight in high pressure blocks remains high. Egg hatch is about 50 percent now. A regional biofix was set for May 16 (250 GDD50 from Jan. 1). GDD since biofix is 520. In problem blocks, cover sprays are crucial to maintain at this time. Expect larval activity for two to three more weeks. Adult trap numbers should begin to decline.

Codling moth adult flight in average/moderate pressure blocks may be at a peak. Egg hatch should be about 30 percent. A regional biofix was set for May 26 (357 GDD50 from Jan. 1). GDD since biofix is 410. In moderate pressure blocks, cover sprays are crucial to maintain at this time. Expect larval activity for two to three more weeks. Adult trap numbers should begin to decline. Accumulated five moths per trap is threshold.

Codling moth adult flight in low pressure blocks with mating disruption continues to be low as expected. A regional biofix was set for June 1 (357 GDD50 from Jan. 1). GDD since biofix is 425. Low pressure blocks and those with longtime mating disruption, delayed cover sprays could be timed for 500 GDD50 or around June 30 (should coincide with obliquebanded leafroller larvae).

Heavy rain should reduce European red mite adults. Continue to assess mites per leaf – they are beginning to build again in some blocks. Threshold is 2.5 mites per leaf for June. Monitor for beneficials – one per leaf indicates wait a week and count again.

Some initial obliquebanded leafroller flight occurred last week. There is a sharp increase in trap numbers this week. A regional biofix was set for June 12 (1,036 GDD42). GDD since biofix is 292. Monitor traps to set your own biofix. The start of egg hatch is estimated for June 30 or so.

San Jose scale adult male flight is complete. A few crawlers have been reported. Timing for targeting crawlers is nearing an end.    Continue to monitor activity.

Oriental fruit moth first generation flight and egg hatch is complete. Second generation adults are beginning to increase slowly. A regional biofix was set for May 6 (256 GDD45). GDD since biofix is 827. Expect second generation flight to increase over the next few weeks. Egg hatch will begin soon. Cover sprays will be needed again around July 4 in blocks with high numbers.

All stages of white apple leafhoppers and potato leafhoppers can be found in average numbers. Continue to monitor.

Green apple aphids are routinely being reported by scouts this week. Woolly apple aphids should be present. Continue to monitor for all aphid species and the beneficials that often attack them.

Spotted tentiform leafminer second generation adults are increasing. Peak flight for second generation is in the next seven to 10 days.

There is a decreasing flight of borers in stone fruits. Dogwood borer adult flight is increasing. Dogwood borer trunk sprays are best timed for peak egg hatch, typically around the 4th of July. Black stem borer first adults trapped May 8, 2015.Trap numbers are declining but adults are still being caught. Continue to monitor.

First reports of rose chafers in apples and stone fruits in sandy sites are coming in to Michigan State University Extension. Continue to monitor.

Some initial flight of spotted wing Drosophila has been reported in various Michigan locations. They are not an issue for apples, but monitoring should be done in soft fruits including cherries, peaches, plums and berries.

There have been no reports of brown marmorated stinkbug egg hatch or nymphs in Michigan. Brown marmorated stink bugs overwinter as eggs, so growers should monitor for nymphs.