West central Michigan tree fruit update – June 5, 2018

Update on tree fruit in west central Michigan.

Weather update

Unseasonably hot weather last week has pushed tree development forward rapidly. Growers have noted that fruit developmental stages that are normally distinctive have blurred together at many locations. Growing degree-day (GDD) accumulations pushed ahead considerably with the heat. West central Michigan is actually running ahead of five-year averages at this time. This is in stark contrast to where the region sat in early May due to the late, cold spring. We have gone from being well behind to slightly ahead of normal.

GDD accumulations for west central Michigan since Jan. 1, 2018

Station

GDD Base 42 F Current

GDD Base 45 F Current

GDD Base 50 F Current

Benona / Shelby

705

572

384

Elbridge / Hart

809

669

466

Hart

785

645

447

Ludington

748

612

420

Crop report

Apples are sizing rapidly across the region. King bloom fruits on early varieties have already sized to 10-plus millimeters at earlier locations. Extreme heat and observations of heavy fruit drop at the 3-6 millimeter fruit stage last week caused many growers to hold off on thinning until a return to more seasonable temperatures. A decent thinning window presented itself for two days in the immediate aftermath of the heat, but after that trees rapidly moved to a state of low stress due to the cool, sunny weather that followed.

Growers attempting to thin this week will need to use more aggressive thinning rates to get the desired results. Although the extreme heat did cause heavy tree stress and considerable drop at some locations, that time of stress is well past now. The vast majority of blocks are carrying a heavy crop and need to be thinned. First generation of codling moth is in flight at this time.

Primary apple scab is nearing an end, but is still ongoing through at least the end of the week. It will likely take at least two more good rains to release the last of the primary scab and bring the season to a close. Keep a good cover up for the rains this week. No reports of fire blight in commercial apple orchards have been received.

Tart cherries are 8-10 millimeters at most locations in the area. The crop looks to be very large at present. No cherry leaf spot damage has been reported in commercial orchards. Two significant cherry leaf spot infection events occurred in the past week, but growers were able to be well covered ahead of the events thanks to good spray conditions both before and after the events.

Growers at first cover are also targeting powdery mildew in addition to cherry leaf spot with fungicide applications, as the powdery mildew fungus typically becomes active around the petal fall timing. No spotted wing Drosophila (SWD) have been detected in the MSU SWD trapline. Plum curculio is still active, but reports of damage have been low in the region.

Peaches are at 6-10 millimeter fruit, depending on location. The crop looks to be heavy at most locations in the region, significant hand thinning may be required to achieve desired fruit size and minimize split pits. Egg hatch of the eggs laid by first generation of oriental fruit moth is ongoing, with a regional biofix for the beginning of flight for the first generation set for May 11.

San Jose Scale male flight started last week, so growers targeting crawlers are looking at applications targeting crawlers at the end of the second or beginning of the third week of June. Heavy flight of lesser peach tree borer and an uptick in greater peach tree borer was observed late last week, prompting many growers to plan a trunk/tree crotch application of Lorsban this upcoming week.

Sweet cherries are at 10-plus millimeter fruit. The crop is highly variable by variety and site. Some varieties look to have gotten too much heat during the heat wave last week and have dropped considerable amounts of fruit. Plum curculio sprays will continue to go out in the early part of this week. The warm, still nights last week were ideal for egglaying, but grower reports of damage have been minimal thus far.

No SWD has been caught in the MSU trapline in the region yet. Bacterial canker on pruning wounds has been minimal this year. Growers who pruned sweets in the spring this year had a good window of dry weather to make cuts, new cuts have generally dried out and healed nicely.

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