West central Michigan tree fruit regional report – June 16, 2015

Heavy rains should lead to the end of primary apple scab.

All tree fruit crops near Grand Rapids, Michigan, are showing a nice crop. There are some sites with a lighter crop and others where hand-thinning will be needed. Heavy rains in the last week provided some much needed moisture, too much in some locations. It came at a time when newly planted trees were just starting to show signs of water stress.

Tree fruit diseases

Several rain events over the past several days have led to one very long infection period for apple scab. At the beginning of the rain event, very low primary scab spore numbers were caught. In the last rain event for the Sparta, Michigan, area, there were no spores, but this rain occurred at night, so primary scab is still on for the Sparta, Michigan, area and north. In Standale, Michigan, we have had two nice daytime rains with zero spores, so it is likely primary scab season is over in areas to the south. For the Hart and Ludington, Michigan, areas, it is likely you might need one or two more rains to discharge any remaining spores, so primary scab fungicide rates are still necessary.

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 or 616-336-4761.

Continue to be on the lookout for flight blight trauma blight symptoms. Overall, blight has been very low in the Grand Rapids, Michigan, area this year.

Powdery mildew is starting to show up a bit more each week. It is not widespread, but as long as shoots are still growing, mildew is a possibility. The recent warm and humid weather is very favorable for mildew.

Tree fruit insects

Codling moth first adult flight in high pressure blocks began May 16. First flight in moderate pressure blocks started May 26. First flight in 10X traps in mating disruption blocks began June 1. Use an early biofix on problem blocks and later for all others. A regional biofix was set for May 26 (357 GDD50 from Jan. 1). GDD since biofix is 307. Problem blocks are at 419 GDD since the May 16 biofix, about 30 percent egg hatch and cover sprays are crucial. Moderate pressure blocks are nearing 20 percent egg hatch. Timing for low pressure codling moths and obliquebanded leafroller hatch should coincide around June 30 this year in low pressure blocks and those with longtime mating disruption.

There are no new reports of plum curculio egglaying in the Grand Rapids, Michigan, area. Areas north could still have activity in stone fruits. Continue to monitor known hot spots.

Some blocks are reporting building or static European red mite numbers. Heavy rain will reduce adults. Continue to assess mites per leaf – they are beginning to build again in some blocks. The threshold is 2.5 mites per leaf for June. Michigan State University Extension advises growers to monitor for beneficials – one per leaf indicates to wait a week and count again.

Some initial obliquebanded leafroller flight occurred last week. There was a sharp increase in trap numbers this week. A regional biofix was set for June 12 (1036 GDD42). GDD42 since biofix is 111. Monitor traps to set your own biofix. The start of egg hatch is estimated for June 30 or so.

Overwintering San Jose scale are present. Adult male flight began around May 23 and should be at a peak. No crawlers have been reported in the west central region, but a few are starting in other southern areas of Michigan. Continue to monitor known hot spots for activity. Crawlers typically appear in mid-June. Use of black electrical tape, sticky side out, on limbs with scale will trap crawlers. Targeting crawlers is the next control window for San Jose scale.

Oriental fruit moth first generation flight is over. Egg hatch should be over for first generation. A regional biofix was set for May 6 (256 GDD45). GDD since biofix is 694. Expect second generation flight to begin soon – this is a good time to change out lures.

New white apple leafhopper nymphs seem to be much easier to find this week compared to last week, but overall numbers are low. We are approaching peak egg hatch this week.

Potato leafhopper adults continue to be found, but numbers are also low, more than likely with last storms. 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 flight is beginning. Continue to monitor.

We are seeing peak flight of borers in stone fruits, so trunk sprays should be started. Some initial dogwood borer flight is being reported. Dogwood borer trunk sprays are best timed for peak egg hatch, typically around July 4.

Black stem borer first adults were trapped May 8.Trap numbers are declining, but adults are still being caught. Continue to monitor.

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