Northwest Michigan fruit update – April 16, 2024

Crop development continues to move along. Growers are preparing to cover green tissue with the rain in the forecast this week.

Honeycrisp apples at green tip.
Honeycrisp at green tip at the Northwest Michigan Horticulture Research Center. Photo by Erin Lauwers, MSU Extension.

Weather report

The weather has been pleasant for the past two days and over the weekend with lots of sunshine. Today, April 16, will start out sunny, but clouds will move in the afternoon and rain is in the forecast for tomorrow. In addition to the rain tomorrow, conditions are predicted to be windy with up to 40 mph winds in the forecast. Following the Wednesday rain, conditions are expected to cool on Thursday with the chance of more rain on Thursday evening. Conditions will dry but are predicted to remain cool over the weekend.

There are some concerns about low overnight temperatures in the forecast with the coldest night/morning predicted to be below freezing on Saturday night into Sunday morning, April 20-21. Growers will need to watch the thermometer and turn on wind machines if these cold temperatures are associated with an inversion. The Williamsburg Enviroweather station is equipped with an inversion tower that can provide growers with information regarding inversion events.

In addition to sun, the region did have a thunderstorm roll through on Saturday night, April 13. This storm brought considerable lightning and some thunder. At the Northwest Michigan Horticulture Research Center, the Enviroweather station reported 0.49 inches of rain. The Bear Lake and Benzonia weather stations reported trace amounts of rainfall that evening. The Williamsburg weather station reported 0.26 inches of rain. The Northwest Michigan Horticulture Research Center area has accumulated 180.9 growing degree days (GDD) base 42 and 60.4 GDD base 50. We are still well ahead of our average of 110.7 GDD base 42 and 43 GDD base 50.

Crop report

Crop development is moving along this season with some warm and sunny conditions over the past few weeks. Montmorency and Balaton are both at side green as of this morning compared to last Friday when Balaton were at early side green, and Montmorency were at bud swell. Sweet cherry are also at side green. Gala are at 0.25-inch green tip, and Honeycrisp are at green tip.

Growers are planting now as trees are starting to be shipped to the region. Some growers are also finishing up with their pruning. There are some bee hives going into orchards now.

Growth stages at Northwest Michigan Horticulture Research Center:

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

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. Leaves may stay wet long enough for infection to occur, even with the colder temperatures expected. The predicted average temperature for Thursday, April 18, is 46.6 degrees Fahrenheit. Approximately 16 hours of wetness are required for primary scab infection at this temperature.

RIMpro links:

Cherry leaf spot. Tarts 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 180.9 GDD base 42 at the Northwest Michigan Horticulture Research Center Enviroweather station.

Dormant oil sprays for pest control (San Jose scale, European red mite, 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.

Oriental fruit moth. First catch of oriental fruit moth were reported at the Trevor Nichols Research Center in Fennville, Michigan, on April 15. We are setting up traplines at the Northwest Michigan Horticulture Research Center for oriental fruit moth and other pests this week in anticipation of their emergence in the coming weeks in northwest Michigan.

Peach leaf curl. 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 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.

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 aphid 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 aphid 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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