Northwest Michigan fruit update – April 2, 2024

There is still some time for dormant and early season pest and disease control in the northwest region, but trees will be moving quickly through growth stages once warm temperatures return.

Weather report

This year’s weather is variable and has been sometimes nerve wracking with the warm and cold conditions over the past few months. However, according to Jeff Andresen, Michigan State University Extension climatologist, we have colder conditions and a snow-rain mix in the forecast for tomorrow, April 3, and Thursday, April 4, but the weather will warm over the weekend and into next week. The medium-range forecast is predicting the weather to be warmer than normal and near to above normal temperatures.

As of today, April 2, we have accumulated 100.9 growing degree days (GDDs) base 42 and 30.5 GDD base 50. In comparing these accumulations to past years, the 2024 data is most like 1998 (Figure 1). These accumulations are ahead of our long-running average at 47.6GDD base 42 and 16.2GDD base 50.

Pest report

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 undersides of branches, and 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. Oils should not be applied during or prior to cold temperatures. Appropriate temperatures are between 40-70 degrees Fahrenheit to avoid phytotoxicity issues. Dormant oils may be applied on apple until pink stage.

San Jose scale. A dormant oil may also be applied to control San Jose scale. Oil may be applied on apple until pink stage, but extra care should be taken the closer to pink it is applied. On sweet cherry, oil can be applied until green tissue is present. An oil application can be highly effective at controlling scale but beware of freezing or extreme temperature fluctuations in the forecast as they may cause phytotoxicity, including overnight freezing temperatures. 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.

Apple scab. The primary infection season of apple scab will begin when we reach green tip. Approximate GDD accumulation for green tip in McIntosh is 127 GDD base 42, which we are calculating this year from Jan. 1. We are currently at 101 GDD base 42 and 127 is beyond the week-out forecast with 109 expected by April 8.

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Cherry leaf spot. Bract leaves have not yet expanded at the Northwest Michigan Horticulture Research Center. Until bract leaves have expanded, fungicide applications are not needed to control this disease. Bract leaf expansion is expected near 250 GDD base 42. We are currently at 101 GDD base 42 at the Northwest Michigan Horticulture Research Center Enviroweather station.

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