Southwest Michigan fruit update – Aug. 25, 2020

Dry weather is slowing development and causing small fruit for most crops but is helping increase sugar content in peaches and grapes.

Apple harvest is underway. Early varieties are being harvested now. Photo by Mike Reinke, MSU Extension.


It was another dry week. Most of the week was cool as well with highs in low 80s and lows in the 50s. Sunday, Aug. 23, saw the start of a short heatwave bringing humid conditions and highs near 90. A cold front is predicted to pass through on Friday, Aug. 28, bringing a chance of scattered rain and highs in the 70s. With a cool week, we picked up fewer growing degree days (GDD) last week: 189 GDD base 42 and 133 GDD base 50, respectively 27 and 19 per day.

Southwest Michigan GDD summary from March 1 – Aug. 23, 2020


GDD 42 F

GDD 45 F

GDD 50 F

Benton Harbor (SWMRC)




Lawton (Lawton)




Fennville (TNRC)




Average for the SW region




Average last week




Tree fruit

Rainfall this summer has been scarce and we are seeing signs of stress in forest trees, ornamental shrubs and some fruit plantings. Codling moth numbers are generally low. Oriental fruit moth and obliquebanded leafroller catches have increased in the last couple weeks. Brown marmorated stink bug adults from the summer generation are being caught in higher numbers. These numbers will continue to build over the next month.

Peaches and nectarines: We are in the PF Lucky 13, Bounty and Canadian Harmony harvest windows in central Berrien County. Recent sunny conditions have promoted relatively high sugar content. Fruit with bacterial spot and insect damage are prone to brown rot and Rhizopus rot. Rhizopus causes a brown colored rot with a loose skin, unlike the relatively firmer brown fruit rot. It forms gray-black sporangiophores on the surface of fruit. Rhizopus is primarily a disease of overripe fruit in storage, particularly if the storage temperature is above 40 degrees Fahrenheit. Brown rot shows up as a fruit rot before and after harvest. The third generation of oriental fruit moth is out now. Western flower thrip is causing white blotches on red blush areas of peaches in some sites.

Peach with scab
Peaches with scab are not very attractive for people to eat, but brown marmorated stink bugs do not have the same reservations. Photo by Bill Shane, MSU Extension.

Cherry harvest is over. Recent dry weather reduced cherry leaf spot infections, but a new wave of yellow infected leaves has appeared the in treetops. To maintain good tree health and winter hardiness, continue to protect the leaves from cherry leaf spot into September. See: Low spray programs for tart cherry.

In plums, harvest of summer plums continues. Castleton harvest is underway. Brown rot is showing up on insect damaged fruit. Plums held on the tree until soft ripe are susceptible to spotted wing Drosophila (SWD) attack.

Apple being harvested include Pristine and Paula Red. Codling moth is still flying in most orchards. Oriental fruit moth numbers are up signaling the start of the third generation adults. Bitter rot is showing up as well as other summer fruit rots. Maintain sooty blotch and flyspeck protection with reapplication when rain has likely reduced coverage. Apple maggot numbers usually peak in August; adult flies emerge after about 0.25 inches of rain. Traps should be placed to monitor susceptible sites. Potato leafhopper burn is pretty common this year in many crops. For our predicted apple harvest dates, see: Predicted 2020 apple harvest dates for southwest Michigan.

Pear Bartlett fruit harvest should start late this week. Codling moth, obliquebanded leafroller and pear psylla are the primary insect pests now. Like apples, pears should be protected against sooty blotch and fly speck.

Small fruit

Spotted wing Drosophila (SWD) numbers are up in southwest Michigan. Collect leaf samples for foliar tissue analysis from mid-July to mid-August.

Grape veraison is complete for most varieties. Most hybrid and vinifera wine grapes are between 12-18 degrees brix. Concord and Niagara are near 11 degrees brix. The disease focus is on reducing the spread of downy mildew and powdery mildew. Downy mildew spreads rapidly when we have heavy dews in the morning. Scout for downy mildew on the leaves and protect healthy leaves from infection. Downy mildew can defoliate the vines in August. Powdery mildew prefers humid warm weather. Powdery mildew seems to be widespread this year. As brix levels increase above 13-15, botrytis bunch rot and sour rot management become more important. Good coverage and chemical class rotation are important for control of both cluster rots. Including an insecticide to manage the insects that spread the disease is particularly effective in managing sour rot.

Grape berry moth is in the middle of the third generation. The grape berry moth model on Enviroweather predicts egglaying began about Aug. 2 in Berrien and Aug. 7 in Van Buren counties. See: August is key time for protecting clusters from grape berry moth. Growers who have had trouble with grape berry moth in the past may need more than one spray. The second spray should be applied about two weeks after the first. It seems likely that we will see a fourth generation this year.

Concord grapes
Some grapes, such as the Concord here, have almost completed veraison. Sugar accumulation has sped up. Many grapes are 12-18 degrees Brix. Photo by Mike Reinke, MSU Extension.

Blueberry harvest continues. Growers are harvesting late season varieties such as Aurora and Elliott. Maintain irrigation after harvest to maintain plant vigor. Growers who are still harvesting fruit need to maintain tight coverage for SWD. SWD really likes cool conditions. In general, many fields look ragged many with red leaves which seem to be a sign of stress

Strawberries in matted rows have filled out the rows and are sending out runners. Growers should maintain protection against potato leafhopper and leaf spot diseases.

In brambles, blackberry harvest continues. Fall raspberry harvest will start soon. SWD is the major insect pest of brambles and can destroy the crop quickly. Treat SWD as a disease and focus on keeping it out. Do not let this pest become established in the field. Pick ripe fruit frequently so that ripe fruit are not available to the pest for long.

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