Southwest Michigan fruit update – Aug. 24, 2021

Apple harvest is beginning.

Fall raspberries ready for harvest.
Fall harvests have begun for many crops. Apples, late peaches and plums, fall raspberries and grapes are now being picked. Photo by Mike Reinke, MSU Extension.


Last week started with cooler, more seasonal conditions with high temperatures in the low 80s, lows near 60 degrees. The temperatures climbed to the upper 80s on Wednesday and remained there for the rest of the week. Despite the humidity, no rain was recorded for the week.

Humid conditions with highs near 90 will continue for the next week. There is a good chance of scattered storms every afternoon.

With warm, humid week, we picked up an above average number of growing degree days (GDD) last week: 221 GDD base 42 and 165 GDD base 50. That is 32 and 24 GDD per day, respectively. We are currently half a week ahead of the five-year average.

Southwest Michigan GDD summary from March 1 – Aug. 22, 2021


GDD 42 F

GDD 45 F

GDD 50 F

Benton Harbor (SWMREC)




Lawton (Lawton)




Fennville (TNRC)




Average for the SW region




Average last week




Tree fruit

Leaf sampling for foliar nutrient content is done from mid-July to mid-August. Nutrient levels are constantly changing in the trees but during this period they are the most stable. Brown marmorated stink bug nymphs and adult catches are still generally low but increasing. Orchard edges, especially bordering woods and buildings, are generally the first locations where this insect can be detected.

Peach/nectarine varieties Fantasia, Glowingstar, Gloria and PF24C are being harvesting in central Berrien County. Oriental fruit moth flight catches are starting to increase, indicating the next generation is likely starting. Adults of the third generation generally emerge in mid-August, depending on the weather. Offspring of this generation is a major cause of wormy fruit at harvest on late season peaches or apples, often with little or no external sign of injury.

Plum varieties Early Italian, Simka and Stanley are close or ready for harvest.

Apple early variety harvests are beginning. Zestar are testing 15.4 pounds of firmness and starch index of 3.0. Main season Gala are testing 20 to 21 pounds of firmness with starch index of 2. Retreatment for sooty blotch and flyspeck is needed following heavy rains.

Apple orchard.
Apple harvest has begun and will become more widespread in the next couple weeks. This is the time of year to be scouting for brown marmorated stink bug. Populations are still low for this pest but are expected to increase soon. Photo by Mike Reinke, MSU Extension.

Pear varieties Bartlett and Harrow Sweet fruit at the Southwest Michigan Research and Extension Center are averaging 17.5 and 18.4 pounds of firmness, respectively, using a pressure tester with 5/16-inch plunger with pear skin off. For Bartlett, firm ripe is 15 to 16 pounds. Harrow Sweet generally harvests one to two weeks after Bartlett.

Small fruit

Spotted wing Drosophila (SWD) numbers are high. Peak populations for this pest are in August and September.

Ripening black cherries.
Spotted wing Drosophila numbers are high. This insect uses lots of wild hosts to build populations. Wild black cherry, ripening now, is one of these hosts. Photo by Mike Reinke, MSU Extension.

In grapes, veraison is well underway. For grape berry moth, May 25-27 (50% wild grape bloom) was grape berry moth biofix in southwest Michigan. The grape berry moth model on Enviroweather predicted egglaying of the third generation began the first week of August. The third generation emerges over a long period of time and can cause significant loss. Treatments that target the second half of this generation may be necessary. Considering how early the third generation started, a fourth generation is likely. This next generation should start in a couple weeks.

Protectant fungicide sprays to control downy mildew, and powdery mildew are the disease focus now. Downy mildew develops rapidly with heavy dews every morning. August is when growers should focus on controlling this disease, which can defoliate the vines before harvest. Rain forecast this week could spread this disease widely in vineyards where there are active lesions. Wine grape growers will want to include botrytis in their disease management plans, especially in tight bunched varieties.

Grapes ready for harvest.
Grape harvest is beginning soon. Downy mildew is a problem this time of year. Keep on top of management for this disease. Photo by Mike Reinke, MSU Extension.

Blueberry harvest is moving quickly with Elliott and other end of season varieties. Many growers are ending their seasons with last pickings as the harvest moves to the northern regions of the state.

SWD numbers increased with the typical August surge. Soils are dry. Growers should increase their irrigation in harvested fields to maintain good plant health and promote flower bud formation at the end of the season.

Strawberry fields are looking good.

Bramble harvest continues. Blackberry harvest is continuing. Fall bearing raspberries harvest is beginning. SWD catches in monitoring traps are high. Fruit needs to be protected as it begins to color and ripen.

Miscellaneous crops

Hop harvest has begun.

Cranberry fruit is coloring.

Upcoming events

Michigan Grape Society will be sponsoring one last evening Grower’s Social event before harvest begins. This event will be hosted by Michigan State University Extension at the Southwest Michigan Research and Extension Center on Thursday, Aug. 26. The event will begin at 6 p.m. with a discussion about season extension and winter protection through the use of high tunnels in grape production. Food and drink will follow. There will be limited attendance. Pre-registration is highly recommended.

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