Southwest Michigan fruit update – May 28, 2024

Warm weather is increasing insect activity in area fruit plantings.

Grape bloom
Concord juice grapes are starting to bloom in southwest Michigan. Photo by Mike Reinke, MSU Extension.


Temperatures in the upper 40s to mid-50s at night and 70s to 80s in the week plus rain on three days during the past week provided good growing conditions for trees and good conditions for fungal diseases.  

Southwest Michigan GDD summary from March 1 – May 27, 2024 


GDD 42 F 

GDD 45 F 

GDD 50 F 

Benton Harbor (SWMREC) 




Lawton (Lawton) 




Fennville (TNRC) 




Grand Junction 




Average for the SW region 




A weather report by Michigan State University meteorologist Jeff Andresen is available online. Note: Due to a family emergency, Andresen will not have a report this week. 

Tree fruit 

Rains over the weekend have helped sandy orchard sites low on water reserves. Based on a biofix of May 6 for catch of San Jose scale adult males at the Trevor Nichols Research Center (Fennville trapline), crawlers from this generation are expected 400 to 450 growing degree-days (GDD) base 51 degrees Fahrenheit later. Current GDD51 sum at the Southwest Michigan Research and Extension Center as of May 27 is 279 and is projected to be 351 by Sunday, June 2. Crawlers are expected by the end of the first week of June in central Berrien County, a bit later than earlier projected due to cooler weather than forecasted. Female San Jose scales examined May 28 at the Southwest Michigan Research and Extension Center were still gelatinous with no differentiated crawlers. Deer feeding on foliage can be a problem on young plantings. 

Apricot fruit (Haroblush variety) are 37 millimeters (mm) in diameter at the Southwest Michigan Research and Extension Center.  

Peach and nectarine midseason harvesting fruit are 38 to 40 mm in diameter. Protection against plum curculio and tarnished plant bug is still needed if there is a crop. Flagging of branch tips by oriental fruit moth larvae damage showed up last week in Berrien County. Rusty spot spray coverage from shuck split to pit hardening is needed for susceptible varieties.  

In cherries, Montmorency tart cherries are still approximately 12 mm in diameter. Fruit growth has been slow during pit hardening, now complete. Cherry leaf spot symptoms are showing up in area orchards. Scouting for symptoms of cherry leaf spot is recommended now to judge effectiveness of your fungicide program. Progibb (gibberellic acid) treatment for prevention of blind wood now helps to maintain fruit production. The Michigan State University Extension Michigan Fruit Management Guide E-154 has more details on treatment.  

In plums, Shiro Japanese plum fruit are 27 mm and Stanley European plum are 25 mm in Berrien County. Fruit drop is underway. Plum curculio is the major insect concern until approximately 1.5 months after bloom. The critical time for fungicide control for black knot is petal fall to approximately late June when new growth slows.  

Apple fruit at the Southwest Michigan Research and Extension Center near Benton Harbor, Michigan, range from 28 to 40 mm in diameter, an increase of approximately 10 mm since last week. Fruit continues to drop due to natural abortion and thinning sprays. Symptoms of nectria twig blight, a fungal disease found on Rome and Northern Spy, can be confused with fire blight. Nectria will often have orange spore masses on wood associated with wilting shoots and cankers. Orchards should be scouted carefully for fire blight now and strikes cut out.  

Apple scab ascospores catches are now ranging in the 10s and 20s per sampling rod compared to the 600s caught in late April. Scab symptoms are easy to spot in some locations. Scouting for scab on leaves, now present in some orchards, will be important in planning fungicide programs. Continued management of powdery mildew and juniper rust is needed for susceptible apple varieties.  

Apple scab symptoms are showing up on leaves. Photo by Linda Davis. 

The sooty blotch and flyspeck model on Enviroweather has recorded 105 hours of wetting starting 10 days after estimated petal fall for central Berrien County. Symptoms for these diseases are expected when the accumulated wetting reaches approximately 240 hours. Codling moth larvae hatch was predicted to start approximately May 21 for central Berrien County.  

Pear (Bartlett) fruit are up to 27 mm and Harrow Sweet 23 mm in diameter at the Southwest Michigan Research and Extension Center. Continued scab sprays are needed to protect green tissue against infection. Pear psylla immature and adult insects are easy to find on fruit and leaves in some blocks and are beginning to cause gumming and sooty deposits. Pear leaf blister mite damage on leaves is showing up. Growth of young trees can be inhibited by severe infestations. 

Small fruit 

Wild grape bloom continues. Secondaries of wild grape are getting close to bloom as well. Wild grape bloom is used as a biofix for grape berry moth. Biofix is when 50% of clusters are at 50% bloom. See this Michigan State University (MSU) Extension article for more information: Using the MSU Enviroweather grape berry moth model in 2018 

An article by Rufus Isaacs and Tim Miles of MSU on dealing with frost-damaged vineyards is now available online. 

Concord and Niagara bloom has begun in much of the area on surviving primary shoots. Advanced hybrid wine grapes are also blooming or very close. Secondary shoots appear to be about two weeks behind primaries in phenology.  

For varieties still a week or more away from bloom, the warm, wet weather we have been experiencing recently and the weather coming up means growers should focus on protecting the developing foliage from phomopsis and early infections of downy and powdery mildew. Phomopsis infections from a couple weeks ago are showing up on foliage.  

For varieties that are immediate prebloom or blooming, the focus should expand to include the spring concerns and the bunch rots: phomopsis, black rot, anthracnose, downy mildew, botrytis bunch rot and powdery mildew. 

In blueberries, green fruit are developing with earlier varieties showing hints of blue. Some farms are reporting poor foliage growth on Bluecrop and other varieties. The cause is unknown so far. Disease control is focused on preventing anthracnose infections to young green fruit. Cranberry and cherry fruitworm have been caught. Second applications of fertilizer are being applied and weed control sprays are continuing.  

Want more blueberry specific content? Subscribe to Blueberry Bites! 

Strawberry harvest is underway in Berrien and Van Buren counties. All the leaves are out by now. Maintain fungicide coverage to protect the leaves and help prevent botrytis as fruit begin to show.  

Upcoming meetings 

Our weekly Monday Night South Michigan Fruit IPM Meetings will are a hybrid format. The meetings will be held in-person at the Southwest Michigan Research and Extension Center, 1791 Hillandale Rd, Benton Harbor, MI 49022, with virtual attendance available online. Our next meeting is Monday, June 3, at 5:30 p.m. No advanced signup is needed for attending in-person. The meetings are free, and one pesticide applicator credit is available for each meeting.  

TheUnconventional Fruit Working Group 01: Orchard and Vineyard Floor Managementwill be May 29 from 12:30 - 1:30 p.m. via Zoom.This is a virtual meetup group for fruit farmers who grow fruit using non-conventional practices, including organic farmers. Each 1-hour meeting has a theme, with the first meeting theme being "orchard and vineyard floor management." After a short educational presentation, farmers can share their experiences and listen to the experiences of other farmers.Sign up here.For more information, contact Derek Plotkowski 

The MSU Controlled Atmosphere (CA) Clinic on July 17 in Muskegon, Michigan, is organized by the MSU Department of Horticulture every other year to pass on new information relating to CA storage and warehousing of apple and other temperate fruit. This will be of primary interest to apple growers and storage operators.  

The meeting this year features four internationally recognized leaders in apple postharvest science: Christopher Watkins (New York), Jennifer DeEll (Ontario), Carolina Torres (Washington State University) and David Rudell (U.S. Department of Agriculture Agricultural Research Service – Wenatchee) and Randy Beaudry (MSU). Sign up here. 

Additional information and surveys    

Michigan State University is running a pollinator survey this spring and summer to understand how people interact with pollinators in natural, urban and managed landscapes. The survey is anonymous and takes only 10-15 minutes to complete.    

This work is supported by the Crop Protection and Pest Management Program [grant no 2021-70006-35450] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.    


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