Northwest Michigan fruit update – April 9, 2024

Weather conditions are currently warm, and crop development is moving along quickly. Growers are covering apples for scab prior to the predicted rain on Thursday and Friday.

A closeup of sweet cherry buds.
Checking on Benton sweet cherry buds during the eclipse on April 8, 2024. Photo by Erin Lauwers, MSU Extension.

Weather report

We have two beautiful warm and sunny days (April 8-9) to start the week following a sunny and windy weekend. On Monday, April 8, we peaked at 66.9 degrees Fahrenheit at the Northwest Michigan Horticulture Research Center. The region did receive trace amounts of rainfall, which was not in the forecast; the Northwest Michigan Horticulture Research Center received 0.07 inches of rain Monday night into Tuesday morning. The region is dry for this time of year, and Michigan State University Extension climatologist Jeff Andresen expects the evapotranspiration rates to be high even if we are predicted to receive 1-1.5 inches of rain Thursday and into Friday.

The weather is expected to cool at the end of the week, and daytime highs are forecasted to be in the 40s F. The weather is predicted to clear over the weekend and be pleasant, sunny and dry. Low temperatures are predicted to be in the upper 30s and 40s over the weekend. The medium range forecast looks for a combination of normal temperatures with normal to above normal precipitation. Watch Andresen’s weekly weather report.

At the Northwest Michigan Horticulture Research Center, we are at 123.5 growing degree days (GDD) base 42 and 38 GDD base 50. We are still ahead of our average GDD accumulations as our long-term average for this time of year is 73 GDD base 42 and 27 GDD base 50.

Crop report

With these two warm days, fruit crops have moved along quickly. We are at side green in both sweet and tart cherries. We have been pruning sweet cherries and removing flower buds in blocks with a big crop, and it is easy to remove them as they are swollen. Honeycrisp are at green tip, and Gala are at 0.25-inch green.

New trees are starting to arrive in the region, and growers are preparing to plant. Many growers, including us, are finishing pruning from the winter season. There is lots of activity in the orchard with spring tasks, and many growers are considering apple sprays prior to the pending rain.

Maximum soil temperatures since April 1 have ranged from 40 – 53 F at the 2-inch soil depth and 40 – 51 F at the 4-inch soil depth at the Northwest Michigan Horticulture Research Center Enviroweather station. Roots start to become active around 45 F and are able to take up water and nutrients. Most fine roots that actively take up water and nutrients are in the top 0.5 – 2 feet of soil, depending on the rootstock.

Pest report

Apple scab

Green tissue will be susceptible to ascospore infection. Apples at green tip should be protected before the rain later this week. Ascospores can be released with a minimum of 0.01 inches of rainfall. The predicted average temperature for Thursday, April 11, is 46.5 F. Approximately 16 hours of wetness are required for primary scab infection at this temperature.

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Cherry leaf spot

Tart cherries at the Northwest Michigan Horticulture Research Center are at side green stage. Prevention of cherry leaf spot infection will be needed when bract leaves emerge. Bract leaf expansion is expected near 250 GDD base 42. We are currently at 126 GDD base 42 at the Northwest Michigan Horticulture Research Center Enviroweather station.

Dormant oil sprays for pest control (San Jose scale, European red mites, woolly apple aphid)

Horticultural oil applied at the delayed dormant stage will control San Jose scale by smothering the overwintering scale. This application would also provide activity against overwintering European red mites in apple. A common way to use dormant oil is 2 gallons per 100 gallons water per acre at green tip in apple and prior to green in sweet cherry. Some growers will break up their oil applications into two sprays: once at green tip with copper and another at 1 gallon per 100 at tight cluster with an insecticide targeting scale and rosy apple aphid. Rates need to be reduced as the oil is applied closer to pink. Spur and bud damage is a high risk at pink and should be reduced to a rate of no more than a gallon of oil per 100.

Dormant oils may be applied on apple until pink stage. Oils should not be applied during or prior to cold temperatures. Appropriate temperatures are between 40 and 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.

Peach leaf curl

Infection of peach leaf curl can occur during bud burst stage until bud opening. The ascospores overwinter on bark and are spread to 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 was severe in many apple and cherry orchards in 2023 due to the dry season and inoculum levels are expected to be high this year. Emerging leaves from buds infected last season will begin to produce conidia and result in an early secondary infection period. Control of this disease at tight cluster until petal fall is critical. The cooler temperature later this week will work in our favor to slow development.

Woolly apple aphid

Live woolly apple aphids have been detected on apple branches on the ridge and in Hart, Michigan. This is an unusual location to find this pest this time of the year. Woolly apple aphids will typically overwinter in the root system and crawl into the tree canopy in spring. Some of the woolly apple aphid population remains in the canopy at the end of the season and is typically killed off by cold winter temperatures. The overwintering woolly apple aphids remaining in the canopy will hide in nooks and crannies of branches.

If you scout for woolly apple aphids, examine pruning scars directly above buds and on the undersides of branches. Look for swollen tissue, nodules and split bark. If you detect any woolly apple aphids, check if they are dead or alive. If living woolly apple aphids are found and you determine control is needed, a dormant oil may be applied.

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