Northwest Michigan fruit update – June 11, 2024

Sweet cherries are starting to color, and more June drop is evident in many sweet cherry varieties. Apples are also sizing, and growers are evaluating their thinning outcomes.

Small unripe cherries
Cherry leaf spot lesions on tart cherry fruit. Photo by Erin Lauwers, MSU Extension.

Weather report 

The weather cooled considerably this weekend and into the early part of this week. Daytime temperatures have barely reached the 60s and nighttime temperatures have been as low as the high 30s in some places. There were even frost warnings for some regions further inland last night, June 10. Fruit growing areas did not frost, but there was considerable dew and low temperatures this morning; the East Leland Enviroweather station recorded a low of 39.7 degrees Fahrenheit this morning.  

The weekend was cold and felt even colder coupled with drizzly and wet conditions. We also had winds yesterday and over the weekend, which likely contributed to it feeling particularly cold the last few days. However, the forecast is expected to drastically change tomorrow. The forecast is predicted to hit 70 F today and reach the 80s on Wednesday and Thursday. The medium range forecast is also expected to be warmer than normal. 

So far this season, we have accumulated 996.8 growing degree-days (GDD) base 42 and 508.6 GDD base 50. We are still well ahead of our long-term average: 837.7 GDD base 42 and 451.1 GDD base 50. 

Crop report 

The following growth stages were evaluated at the Northwest Michigan Horticulture Research Center yesterday morning, June 10: 

  • Balaton – 13 millimeters (mm) 
  • Bartlett Pear – 16 mm 
  • Montmorency – 13 mm 
  • Potomac Pear – 23 mm 
  • Emperor Francis – 15 mm 
  • Gold – 12 mm 
  • Ulster – 15 mm 
  • Riesling – 10-16" shoots 
  • Gala – 22 mm 
  • Honeycrisp – 25 mm 

We are observing a considerable drop in sweet cherries at the Northwest Michigan Horticulture Research Center. We have also been hearing reports of drop from growers. Watch fruit that is intended to drop but may get caught in clusters and be a potential site for American brown rot infection. This year has been good for diseases due to the consistent moisture and high humidity, and brown rot is no exception—this disease is favored by warm and wet conditions and can be especially problematic in tight clustered varieties. 

Apples are sizing well with the moisture and cool conditions. Shoots are also growing rapidly under these conditions, and growers need to manage shoot growth aggressively this season. Many growers have been using prohexadione-calcium (PCa) (Apogee/Kudos) on a regular program to reduce shoot growth and to minimize impacts from potential shoot blight infections. Under optimal growing conditions, it will be important to continue with these PCa programs. Growers should also be managing bitter pit, particularly in Honeycrisp. Todd Einhorn, associate professor in the Department of Horticulture at Michigan State University, also thinks NAA now and again at 45 – 50 days after bloom would be beneficial.  

Pest report 

American brown rot. Warm and wet conditions are favorable for American brown rot growth. Cracking from rain or wounding from bird damage or bacterial canker infection in sweet cherries leads to higher likelihood of brown rot infection. As fruit gets closer to harvest, susceptibility to brown rot increases. Consider if brown rot management is needed. Using Indar may not be effective, even at the highest labeled rate of 12 ounces per acre. Previous research and resistance screening of American brown rot isolates in west central and northwest regions found that most screened fungal isolates had functional resistance to Indar. Find more information about this study. Effective materials for managing American brown rot include Merivon, Miravis and Cevya. Full coverage of all rows will be important to manage this disease. 

Apple scab. Primary scab season has concluded. Orchards should be scouted for lesions to determine risk of secondary infection; some lesions have been observed in blocks at the Northwest Michigan Horticulture Research Center. Disease management must continue if lesions are present. RIMpro also includes figures for secondary scab. To view, use the following links and select the “Scab Secondary” tab at the top of the webpage.  

RIMpro links:    

Bacterial canker. The cool and wet conditions this season have been highly favorable for growth of the bacterial canker pathogen. Reports of shot-hole leaf symptoms and water-soaked lesions on fruit are widespread in the northwest and other regions of the state. Cherries damaged by canker will be susceptible to American brown rot (see above).  

Cherry leaf spot. Severe cherry leaf spot infection and early defoliation has been reported in some blocks in the region. Lesions have even been observed on cherry fruit and stems. Keeping cherries protected against infection is crucial this year given the favorable conditions and prolonged disease season. Copper is a great material for managing cherry leaf spot when temperatures are below 80 F. Recommended rate for cherry leaf spot management is 1.2 pounds metallic copper per acre.  

Fire blight. Shoot strikes have been reported in a few blocks in both southeast and Grand Rapids, Michigan, areas. Shoots in a pathology research block at the Northwest Michigan Horticulture Research Center are beginning to ooze and show symptoms of necrosis and flagging. Timely pruning of infected shoots is highly recommended to prevent systemic movement of the bacteria. Shoots should be pruned 12-18 inches below the symptomatic tissue into 2 year or older wood. Leaving a 2- to 3-inch stub has been shown to reduce the number of cankers in the structural wood (trunk).  

Powdery mildew. Orchards should be scouted for secondary infection of powdery mildew. If symptoms are observed, management of this disease must continue. Powdery mildew has been reported in all areas of the state on apple. Symptoms have not been seen on tarts yet at the Northwest Michigan Horticulture Research Center. 

American plum borer. An average of 1.6 American plum borer were caught this week at the Northwest Michigan Horticulture Research Center.  

Black stem borer. An average of 13 black stem borer were caught this week at the Northwest Michigan Horticulture Research Center. 

Codling moth. An average of 13.3 codling moths were trapped this week. The biofix for codling moth in northwest Michigan is May 17. All northwest Enviroweather stations except Northport have reached the timing for larvicidal treatments (250 GDD base 50 F) based on the estimated biofix. Northport is estimated for June 15.  

Greater peach tree borer. Zero have been caught at the Northwest Michigan Horticulture Research Center. 

Green fruitworm. Zero were trapped at the Northwest Michigan Horticulture Research Center.  

Lesser peach tree borer. An average of six lesser peachtree borer were trapped at the Northwest Michigan Horticulture Research Center.  

Obliquebanded leafroller. Adults were trapped for the first time this year in cherry and apple blocks at the Northwest Michigan Horticulture Research Center. The biofix will be set for next week if we have sustained catch.  

Oriental fruit moth. Zero were caught this week at the Northwest Michigan Horticulture Research Center. 

San Jose Scale. An average of 3.3 San Jose scale male flyers were trapped this week. This year’s biofix is May 18. Crawler emergence is predicted for 400 – 450 GDD base 51 after biofix. We have accumulated 264.7 GDD base 51 so far. Managing this target is most effective during the first-generation crawler stage.  

Spotted tentiform leafminer. None were caught at the Northwest Michigan Horticulture Research Center. 


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