Northwest Michigan fruit update – June 25, 2024

Weather conditions in northwest Michigan are ideal for many pests this season and keeping trees protected is a challenge with the frequent rain events.

Brown and withered, infected cherry hanging from a tree.
Sporulation of American brown rot on sweet cherry cluster. Photo by Erin Lauwers, MSU Extension.

Weather report 

The heat dome that covered much of the Midwest last week is moving on and leaving us with some slightly cooler temperatures. Today, June 25, is predicted to be the warmest day of the week with a high of 83.1 degrees Fahrenheit. Wednesday, June 26, will feel refreshing in comparison with a high of 66 F. The remainder of the week is expected to see averages in the mid- to upper 60s.

Many areas of the northwest region accumulated a significant amount of rainfall over the weekend; we had 1.52 inches of rain Saturday, June 22, at the Northwest Michigan Horticulture Research Center. Severe weather overnight from June 24–25 brought another 0.43 inches of rain and potential damage from high winds. The Benzonia Enviroweather station measured a total of 2.58 inches since June 22. More rain is expected late this week beginning Friday, June 28, into Saturday.

We have accumulated 1,369.5 growing degree-days (GDD) base 42 and 771.1 GDD base 50. We are still ahead of our average: 1,179.4 GDD base 42 and 681.8 GDD base 50.

Crop report

The following growth stages were evaluated at the Northwest Michigan Horticulture Research Center yesterday morning (June 24):

  • Balaton – 17 millimeters (mm)
  • Bartlett Pear – 21 mm
  • Montmorency – 20.5 mm
  • Potomac Pear – 30 mm
  • Emperor Francis – 20.5 mm
  • Gold – 18 mm
  • Ulster – 22.5 mm
  • Riesling – 80% bloom
  • Gala – 31 mm
  • Honeycrisp – 34.5 mm

Some fruit cracking has been observed following the rain over the weekend. There are concerns about fruit and limb damage after the high winds on June 25. The frequent rain this season presents a challenge to keeping trees protected against disease and insect pests.

Pest report

American brown rot. Sporulation on sweet cherries has been detected this week and weather conditions are favorable for American brown rot growth. Cracked cherries from rain this past weekend and overnight June 24 will increase risk of infection as well as bird damage and bacterial canker infection. As fruit gets closer to harvest, susceptibility to brown rot increases.

Growers need to be diligent about controlling American brown rot in sweet cherry. Using 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. Disease management must continue if lesions are present. RIMpro also includes figures for forecasting secondary scab. To view, use the following links and select the “Scab Secondary” tab at the top of the webpage.

RIMpro links:     

Bacterial canker. Leaf and fruit lesions from bacterial canker are prevalent in orchards this season. 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 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. 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. Trauma blight is a concern after the severe weather on June 25. Broken limbs from high winds or damage from hail will put apples at risk for fire blight infection. 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. 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- to 3-inch stub has been shown to reduce the number of cankers in the structural wood (trunk).

Fruit rot. Humid and warm nights are favorable for apple fruit rot infections including black rot and bitter rot. Mummies leftover from last year can serve as inoculum sources and fruit damaged in the current season can be colonized and increase inoculum. Intervals for fungicide applications should not be extended past 10 days. Merivon is the best fungicide for fruit rot control with up to four applications per season. It is recommended to save one application for directly before harvest. Thiophanate-methyl is a good option for controlling black rot in particular. Fruit should be cooled down as soon as possible after harvest to decrease the development of rots in the bin.

Powdery mildew. Powdery mildew has been observed on tart cherry leaves. 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.

Sooty blotch and fly speck. It is still early for visible symptoms of sooty blotch and fly speck. High temperatures and frequent rainfall with high humidity favor these diseases. First spray for sooty blotch can be timed after 300 hours of leaf wetness (3 hours duration or longer) are accumulated since 10 days after petal fall. So far, we have accumulated 173 hours since May 27.

American plum borer. An average of 1.3 American plum borer were caught this week at the Northwest Michigan Horticulture Research Center.

Black stem borer. An average of two 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 13 codling moth 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 peak egglaying (550 GDD base 50 F) occurred June 24 at the research center. Be cautious of codling moth because these pests prefer to fly at dusk when temperatures are warm. Now that we have warm and wet conditions, codling moth flight and activity will increase; the remainder of the first-generation egglaying is yet to be complete.

Greater peachtree borer. An average of 1.6 greater peachtree borer have been caught at the Northwest Michigan Horticulture Research Center.

Lesser peachtree borer. An average of 31.6 lesser peachtree borer were trapped at the Northwest Michigan Horticulture Research Center.

Obliquebanded leafroller. Biofix was set June 17 for Northwest Michigan Horticulture Research Center. The beginning of egg hatch (the beginning of typical treatment timing) is expected June 29 (350 GDD base 42 after the biofix).

Oriental fruit moth. We caught zero oriental fruit moth this week at the Northwest Michigan Horticulture Research Center.

San Jose scale. Zero San Jose scale male flyers were trapped this week. The Northwest Michigan Horticulture Research Center reached 400 GDD base 51 after the biofix on June 18, the expected time for crawler emergence. Crawlers have not been trapped yet at the Northwest Michigan Horticulture Research Center. Managing this pest is most effective during the first-generation crawler stage.

Spotted tentiform leafminer. An average of 66.6 spotted tentiform leafminer were caught at the Northwest Michigan Horticulture Research Center.

Spotted winged drosophila. Conditions are optimum for spotted wing drosophila development. Traps set on Friday, June 21, and checked on Tuesday, June 25, had a total of 342 flies. Trap count obviously indicates that numbers are rising, and with more wet and warm temperatures in the forecast, we do not foresee a slowdown in population growth.


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