Northwest Michigan fruit update – June 18, 2024

Hot and wet weather are in the forecast. Growers are gearing up to cover ripening fruit to control insects and fungal diseases. Spotted wing drosophila has been caught in cherry and strawberry blocks.

Weather report 

After the cool and wet weather last week, the forecast is predicting hot and wet weather. There is a heat dome settling over the Midwest and Northeast, and there are very hot temperatures in the forecast. There are heat warnings in many major cities across these regions. Traverse City, Michigan, is predicted to hit 90-plus degrees Fahrenheit today, June 18. Tomorrow is also predicted to be hot again. There is also rain in the forecast for Thursday, Friday, Saturday and even into Sunday (June 20-24); the chance of rain is 50–60% but that could change with the forecast. Also, with the hot weather, there is a higher chance for more severe weather. Conditions are predicted to be humid through the weekend. Next week will be cooler and drier.  

According to Jeff Andresen, the medium range forecast is calling for warmer than normal temperatures to near to above normal precipitation totals. We have accumulated 1176.2 growing degree-days (GDD) base 42 and 633.6 GDD base 42. We are still head of our average: 999.2 GDD base 42 and 560.2 GDD base 42. 

Crop report 

The following growth stages were evaluated at the Northwest Michigan Horticulture Research Center yesterday morning (June 17): 

  • Balaton – 14 millimeters (mm) 
  • Bartlett Pear – 17 mm 
  • Montmorency – 14 mm 
  • Potomac Pear – 24.5 mm 
  • Emperor Francis – 16.5 mm 
  • Gold – 13 mm 
  • Ulster – 17 mm 
  • Riesling – 10–16-inch shoots 
  • Gala – 25 mm 
  • Honeycrisp – 28.5 mm 

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. With warm and wet conditions in the forecast, growers will need to be diligent about controlling American brown rot in sweet cherry. The use of Indar is not 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. Growers should also slow down and use full labeled rates to ensure full coverage of fruit clusters.  

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 have been reported 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, and this observation is rare. Keeping cherries protected against cherry leaf spot infection is crucial this year given the favorable conditions and early start of the season; at the Northwest Michigan Horticulture Research Center, we observed open bract leaves on April 26. So far this season, we have had four low cherry leaf spot infections, three moderate infections and two high infections. In addition, we have seen high levels of relative humidity this season. Copper is effective for managing cherry leaf spot when temperatures are below 80 F. The recommended rate for cherry leaf spot management is 1.2 pounds metallic copper per acre. Captan is also a good cherry leaf spot material. 

Fire blight. Timely pruning of infected shoots is highly recommended to prevent systemic movement of the bacteria. Infected shoots should be pruned in a timely manner, removed and destroyed to prevent further spread within a tree and decrease inoculum sources. The best management practice for shoot removal is to cut 12–18 inches below the symptomatic tissue into 2-year or older wood. Leaving a 2–3-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. We are also seeing some mildew showing up on new growth in tart cherry. 

American plum borer. An average of 0.6 American plum borer were caught this week at the Northwest Michigan Horticulture Research Center.  

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

Cherry fruit fly. Zero were trapped this week at the Northwest Michigan Horticulture Research Center. 

Codling moth. An average of 11 codling moths were trapped this week. The biofix for codling moth at the Northwest Michigan Horticulture Research Center is May 17. See the codling moth GDD model on Enviroweather. The model is reporting first generation at 20% egg hatch (350 GDD base 50 F) occurred on June 14 at the research center. Growers should be cautious of codling moth because these pests prefer to fly at dusk when temperatures are warm. We have had cooler dusk and overnight temperatures prior to this heat, and now that we have warm and wet conditions, codling moth flight and activity is likely to increase; the remainder of the first-generation egglaying is yet to be complete. 

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

Lesser peachtree borer. An average of 16 lesser peachtree borer were trapped at the Northwest Michigan Horticulture Research Center.  

Obliquebanded leafroller. Biofix is set for June 17 at the Northwest Michigan Horticulture Research Center if sustained catch. The beginning of egg hatch (typical treatment timing) is expected 350 GDD base 42 after the biofix.  

Oriental fruit moth. We caught 0.66 oriental fruit moth 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. The Northwest Michigan Horticulture Research Center is predicted to reach 400 GDD base 51 on June 18. Management of this target is most effective during the first-generation crawler stage.  

Spotted tentiform leafminer. An average of 5.3 spotted tentiform leafminer were caught at the Northwest Michigan Horticulture Research Center. 


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