Southwest Michigan fruit update – Aug. 21, 2018

Apple harvest is beginning. Peach and plum harvest continues. Blueberry harvest is ending.


Temperatures last week were normal for August, with lows in the mid-60s and highs in the mid-80s. Scattered rain over the weekend dropped a trace to over an inch. Rainfall totals for the season range from 18 to 22 inches, so southwest Michigan has missed the dry conditions affecting the rest of Michigan. Scattered showers crossed the region Monday, Aug. 20, but it dropped less than an inch. We are about a week ahead of normal for the season.

Weather for the upcoming week should be cooler with highs in the 70s and no rain until the weekend. The following week will bring a return to hot weather into September.

Southwest Michigan GDD summary from March 1 – Aug. 20, 2018


GDD 42 F

GDD 45 F

GDD 50 F

Benton Harbor (SWMRC)




Lawton (Lawton)




Fennville (TNRC)




Average for the SW region




Accumulation last week




Tree fruit

San Jose scale trap catches are just starting to decline in this fifth week of the summer generation. Apple maggot numbers have been high for four weeks, but are now starting to decline. Insecticide choices should include materials effective against apple maggot. Brown marmorated stink bug adult numbers are still relatively low compared to last year at this time. Spotted wing Drosophila numbers are high.

Peach and nectarine harvest of Allstar, PF 17, Sweetstar, Messina and Coralstar is underway in Berrien County. Flavor and skin color has been good. Rainfall has been adequate in sites with heavier soils and better water reserves, but not sufficient in sandier sites. Fungicide treatments for brown rot are needed as fruit background color loses its green color. Leaf drop of older leaves due to bacterial spot infection is common on susceptible varieties.

Oriental fruit moth numbers declined this week compared to last week. This is the third generation flight. Growers who deployed pheromone disruption for oriental fruit moth around bloom time may see increased pressure from this insect as the lures start to wear out. Sprayable pheromones are available to extend the period of control. Peaches are especially attractive to brown marmorated stink bugs, causing white regions of slightly firmer, disorganized peach flesh close to the skin.

Loss of cherry leaves due to cherry leaf spot continues in area orchards. Some orchards have been virtually defoliated. Maintain fungicide protection to preserve the remaining leaves. August is a common time to see slight wilting, drought-like symptoms of tart cherry trees infested with the brown American plum borer larvae in the crown area.

Plum harvest of Rubyqueen, Castleton and Fortune is beginning in some orchards. Continue protection against brown rot. Protect ripening plums against apple maggots. Apple maggot numbers have been high for over a month, but are starting to decline in traps at the Trevor Nichols Research Center. Codling moth and oriental fruit moth can also attack plums.

Spotted wing Drosophila can attack plums as they ripen, with their thin skins and soft flesh. Plums become susceptible when they soften to approximately 3 pounds firmness, measured without skin. Use a fruit firmness gauge fitted with a pear tip.

Apple harvest of Zestar, Ginger Gold and Paula Red continues. We are testing apple maturity using starch conversion on the Cornell University scale. Traditional Gala harvest will not be for a while, early strains such as Wildfire are expected two to three weeks sooner.

Weather conditions over the past two weeks have been only moderately favorable for sooty blotch and fly speck. Black rot, frogeye leafspot and rust leaf spot symptoms are relatively common this year in apple plantings where fungicide programs have been inadequate.

European red mite levels have reached leaf bronzing levels, especially where pyrethroids have been used. Catches of oriental fruit moth and codling moth adults continue at relatively low levels in in most orchards. Obliquebanded leafroller is also flying and egg hatch has begun. Apple maggot trap catch numbers are starting to decline in the Trevor Nichols Research Center trap line.

Pear harvest of Bartlett will begin at some orchards over the next week. Black leaf symptoms due to European red mite are being noticed. Pear fruit become attractive to codling moth attack when they soften close to harvest in August. Pears need to be protected from the second generation flight, which is occurring now.

Small fruit

Grapes are in veraison. Berries are softening and coloring. We are seeing increased powdery mildew and downy mildew on the leaves. Downy mildew will be a problem as heavy morning dews become common. Protect the leaves of susceptible varieties. Botrytis and sour rot symptoms are apparent in some clusters with insect damage, cracked berries or other diseases.

Third generation grape berry moth egglaying continues and we are beginning to see some active feeding. Check vineyards and consider additional control of the third generation. Insecticides with good contact activity are the best options for this tactic. Most of the damage is at vineyard edges near adjacent areas with wild grapes. Growers and managers may be able to use border sprays as the damage is concentrated on vineyard borders adjacent to woods that contain wild grape. This is not a good option for growers who need to protect leaves from downy mildew or knock back powdery mildew in the vineyard.

The number of spotted wing drosophila (SWD) flies in traps is still increasing, and now that veraison is rapidly approaching, check vineyards regularly to decide whether treatment is needed for SWD and other native vinegar flies that infest ripe clusters. Here again, border sprays might be an option for vineyards with rows parallel to woods.

We are starting to see brown marmorated stink bug in some vineyards, and there are reports of increasing brown marmorated stink bug numbers in other crops in southwest Michigan. Look for this insect until harvest. A clean-up spray using a contact insecticide with a short pre-harvest interval may be required to knock down brown marmorated stink bugs from clusters before harvest.

Blueberry harvest is winding down quickly. Many growers finished early. Growers with fruit are applying fungicides and insecticides to protect ripening fruit against fruit rots and spotted wing Drosophila (SWD). SWD numbers are high. Maintain irrigation to maintain bush health and set the plants up to set a good crop of flower buds for next year. During summer, blueberry fields need an inch of water a week.

Strawberries should be protected from leaf diseases and potato leafhopper, which stunt plant growth. Maintain irrigation to assure good yields next year.

Bramble harvest continues. Fall raspberry harvest is underway. Raspberry are a preferred host for spotted wing Drosophila and the fruit always needs to be protected.

Upcoming meetings

The annual Trevor Nichols Research Center Field Day is Tuesday, Sept. 25, 2018, from 1 to 4 p.m. at the Trevor Nichols Research Center west of Fennville, Michigan.

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