Northwest Michigan fruit update – April 23, 2024

First white is starting to show on sweet cherries. Tart cherries are in bud burst. Weather forecasts are concerning, with cold overnight temperatures predicted for the next two nights.

Sweet cherries blooming.
Sweet cherry at early white bud at the Northwest Michigan Horticulture Research Center. Photo by Erin Lauwers, MSU Extension.

Weather report

The most notable issue regarding weather is the predicted cold temperatures that are in the forecast for Wednesday and Thursday evenings, April 24 and 25. According to Jeff Andresen, Michigan State University climatologist, northwest Michigan is predicted to be colder than other areas of the state. There is even some snow in the forecast during Wednesday evening. There is currently rain on and off across the region, and there are potential thunderstorms developing in the afternoon today, April 23. The cold front will move into the region on Wednesday, and both Wednesday and Thursday are predicted to be cold.

In addition to cold temperatures, the dew point will be low and it will be dry. Temperatures will start out in the 50s today and drop into the 40s for daytime highs; nighttime temperatures will drop into the mid-20s in northern Michigan and in the 30s further south. The weather will warm on Friday and throughout the weekend. Some forecasts are calling for daytime highs of 75 degrees Fahrenheit for Traverse City, Michigan. This warmer weather will also be coupled with precipitation.

The medium range forecast is calling for warmer and wetter conditions than normal for the next one to two weeks. Conditions for the longer-term forecast are also calling for warmer than normal temperatures for the growing season.

We have accumulated 218 growing degree days (GDD) base 42 and 148 GDD base 50 so far this season. We are still ahead of our long-term average of 72.7 GDD base 42 and 58.7 GDD base 50. With the warmer weather, we are catching up to our average with the accumulations base 50.

Crop report

The following growth stages were evaluated at the Northwest Michigan Horticulture Research Center yesterday afternoon, April 22:

  • Balaton – tight cluster
  • Bartlett Pear – green cluster
  • Montmorency – bud burst
  • Potomac Pear – late green cluster
  • Emperor Francis – early white bud
  • Gold – tight cluster
  • Ulster – early white bud
  • Riesling – early bud swell
  • Gala – tight cluster
  • Honeycrisp – tight cluster

Growers are concerned about the upcoming cold temperatures in the forecast and wondering about when/if to turn on frost fans. According to Andresen, the cold temperatures in the forecast could be a mixed bag of freeze events, both advective and radiative freezes. Advective freeze events occur when cold and dry air blows into a region from elsewhere whereas radiative freezes happen when clear, calm conditions allow heat to escape from the earth’s surface and drop the local temperature.

Radiative freezes often have a warmer layer of air above the surface called an inversion—inversions create a situation where frost fans are useful in mixing the warm and cold airs to reduce potential freeze damage. However, advection freeze events do not have a warm and cold layer, and are often associated with wind; therefore, wind machines/frost fans are not effective against this type of freeze event.

Keep an eye on Enviroweather stations across the region and make the call to turn on frost fans if an inversion is present. The Williamsburg Enviroweather station has a tower, and growers can determine if frost fans will be beneficial. “What can fruit growers do if a freeze is coming?” from Michigan State University Extension is a good article for preparing for the upcoming cold overnight temperatures.


Pest report

With warmer temperatures, there has been a lot of pollinator activity over the past few days. Commercial honey bee and bumble bee hives have been arriving in orchards in northwest Michigan for the pollination of cherry and apple. Honey bees will forage at temperatures of 65 F or warmer. Bumble bees and solitary bees will forage at temperatures five to 10 degrees cooler than honey bees.

As we approach bloom, implement practices that minimize pesticide exposure to bees by using reduced risk pesticides and spraying at times when pollinators are not active. Find tips and guidelines to minimize bee pesticide exposure in the article “Pollinator stewardship during fruit crop bloom.”

Apple scab. We are moving to a pretty wet weather pattern with multiple weather systems with precipitation moving across northwest Michigan today, the end of the week and over the weekend. Apples should be covered now to protect against primary scab infection, especially with the return of warmer temperatures over the weekend, which will speed up ascospore maturation and decrease the number of hours of leaf wetness required for infection. The predicted average temperature for Saturday, April 27, is 60.1 degrees Fahrenheit at the Northwest Michigan Horticulture Research Center. Only 9 hours of wetness are required for primary scab infection at this temperature. The accumulated precipitation from the multiple weather systems is expected to be 1-2 inches, so apples should be recovered after these storms are gone. Lots of new tissue is also expected to emerge this weekend that will need to be covered before the next rain.

The RIMPro output for all northwest weather stations is predicting increasing infection risk. East Leland is predicted to reach “Extreme infection risk” starting April 29. Disease management is recommended when the RIM infection value exceeds “slight infection risk.”

RIMpro links:

Brown rot. Brown rot blossom infection will be of concern once we reach white bud in sweet cherry and pink bud in peaches. Warm and wet conditions are ideal for its growth and warmer weather will be returning after the cold weather system this Thursday.

Cherry leaf spot. Tarts at the Northwest Michigan Horticulture Research Center are at bud burst stage. Prevention of cherry leaf spot infection will be needed when bract leaves emerge. The wet weather and warm temperatures in the forecast will be optimum for cherry leaf spot infection. Bract leaf expansion is expected near 250 GDD base 42, which we are forecasted to reach on Saturday, April 27. We are currently at 217.9 GDD base 42 at the Northwest Michigan Horticulture Research Center Enviroweather station.

Dormant oil use. Dormant oils should be avoided due to the forecast's low temperatures. Appropriate temperatures are between 40-70 F to avoid phytotoxicity issues. Oils should not be used 48 hours before or after a frost event and sulfur or Captan should not be applied within five days of an oil application. After the threat of low temperatures passes this week, dormant oils may be applied on apricot until first bloom, apple until pink stage, pear until bud burst, peach until pink and cherry until white bud.

Fire blight. Blossom blight infection of fire blight should be kept in mind as we approach apple bloom. The Enviroweather fire blight model can be used to assess infection risk potential by choosing your closest weather station and entering date of full bloom.

Green fruitworm. An average of nine green fruitworm were caught at the Northwest Michigan Horticulture Research Center.

Oriental fruit moth. No oriental fruit moth were caught this week at the Northwest Michigan Horticulture Research Center. First catch of oriental fruit moth were reported at the Trevor Nichols Research Center in Fennville, Michigan, on April 15.

Peach leaf curl. Peach leaf curl was reported in central Indiana, which is approximately three to four weeks ahead of northwest Michigan phenologically. Infection of peach leaf curl can occur during bud burst stage until bud opening. The ascospores overwinter on peach tree bark and are spread to the buds by rain. Long periods of cool, wet weather favor severe infection. A fungicide should be applied at or before bud break to prevent infection.

Powdery mildew. Powdery mildew sporulation on peaches in southwest Michigan was observed this week by Bill Shane. Although this disease is not of primary concern for now with the rainy weather in our forecast, powdery mildew was severe in many apple and cherry orchards in 2023 and inoculum levels are expected to be high this year. Managing this disease will become critical if dry conditions return during tight cluster to petal fall. Emerging leaves from buds infected last season will begin to produce conidia and result in an early secondary infection period.

Spotted tentiform leafminer. Adult spotted tentiform leafminer was caught in one of the three apple orchards being monitored at the Northwest Michigan Horticulture Research Center.

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