Northwest Michigan fruit update – May 28, 2024

The northwest region received over 1 inch of rainfall, and the moisture and cooler temperatures has resulted in tremendous tree growth. Growers will need to reapply materials to protect against diseases and insects after this rain.

Cherry leaves with an insect larvae.
Obliquebanded leafroller larva on tart cherry leaf. Photo by Erin Lauwers, MSU Extension.

Weather report

The most noticeable weather event was Memorial Day’s (May 27) day-long rain event. The Enviroweather at the Northwest Michigan Horticulture Research Center recorded 1.2 inches of rain on Monday with a bit more on Tuesday morning. We also received 0.25 inches of rain on Saturday, May 25. Overall, the region received variable amounts of rain: Eastport received 3.13 inches of rain and Bear Lake only received 0.18 inches of rain. Most of the other stations received about an inch of rain, but Benzonia received 0.45 inches and Northport received 1.96 inches. The region is extremely green and lush, and lawns and fruit trees are growing fast. If there was a good year for the Apogee plus Actigard to keep tree growth and potential shoot blight in check, this year is it!

In addition to the rain, the weather has been cool. Daytime highs have been in the mid-60s to low 70s. Nights have also been cool, and temperatures have dipped down into the 40s and 50s. There is a particularly cool night in the forecast this week, and the temperature is predicted to drop to 41 degrees Fahrenheit in Traverse City. This overnight temperature is likely to be colder in more inland areas of the state.

So far this season, we have accumulated 727.6 growing degree-days (GDD) base 42 and 347.7 GDD base 50. We are still well ahead of our long-term average: 552.4 GDD base 42 and 347.7 GDD base 50. With the cool weather this week, we are likely to move back to a more normal amount of accumulation.

Crop report

The following growth stages were evaluated at the Northwest Michigan Horticulture Research Center on May 28:

  • Balaton – 12 millimeters (mm)
  • Bartlett Pear – 10 mm
  • Montmorency – 11-12 mm
  • Potomac Pear – 16 mm
  • Emperor Francis – 13 mm
  • Gold – 11 mm
  • Ulster – 13.5 mm
  • Riesling – 10-16-inch shoots
  • Gala – 11-12 mm
  • Honeycrisp – 13-14 mm

Again, growers need to be using Apogee and Actigard to protect against shoot blight and reduce shoot growth in apples. The apples are growing fast with this wet weather, and fire blight can be more problematic in new growth; these shoots are much more susceptible to shoot blight, particularly if we have extreme weather events, such as wind and/or hail. In 2018, another season where we had excessive shoot growth, we had a lot of shoot blight on tender fast-growing shoots—even without a hail event, we had shoot blight with winds that caused enough damage to allow the bacteria to move into the shoot.

We are almost past the time to use Pro-Gibb for keeping trees in balance. We were at five to seven open leaves last week here at the Northwest Michigan Horticulture Research Center, and most areas are beyond this window. Additionally, this cool weather will result in less activity from plant growth regulators (PGRs).

Growers will also have a challenge when thinning with this cool weather. The best thinning weather is cloudy and warm, which is not in the forecast until the weekend and into next week. We are also moving out of the window for thinning with the apple fruitlets growing so rapidly. At the Northwest Michigan Horticulture Research Center, Gala are at 11-12 mm and Honeycrisp are at 13-14 mm. The optimal size to thin apples is between 8-10 mm, and we are approaching a time when apples cannot be chemically thinned from the trees. We applied thinners at the Northwest Michigan Horticulture Research Center last Friday, and we hit them heavier than usual knowing this cool weather was coming this week. Again, Accede is a new product labeled in apples that has been shown to remove fruit at a larger size than our standard thinning applications.

Pest report

Apple scab. Ascospores continue to be trapped in southwest Michigan and the Grand Rapids region, indicating primary scab season is still under way. The disease model on Enviroweather shows an ongoing wetting event for the Northwest Michigan Horticulture Research Center since Sunday, May 26. Many spores were likely discharged during this span and have had ample time to germinate and infect. Leaf lesions from wetting events earlier this season are beginning to show up in northwest Michigan.

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Cherry leaf spot. Lesions from primary infection are already becoming visible on tart leaves; this is going to be a long season for managing secondary cherry leaf spot infections. The warm and humid/wet weather in northwest Michigan continues to favor cherry leaf spot development and if unmanaged, disease pressure may become extremely high by the end of the season. Tarts and sweets should be protected.

Fire blight. Most varieties of apples are past bloom, bringing an end to blossom blight season and the beginning of shoot blight season. The epiphytic infection potential (EIP) has decreased due to having colder temperatures the past few days. High winds have been common this season and could result in trauma blight. New shoots are growing rapidly, and this tissue is very tender and therefore susceptible to wounding. The bacteria can then enter the plant and cause infection through these wounds. Conditioning trees against shoot blight infection with 2 ounces Apogee and 1 ounce Actigard per 100 gallons every seven to eight days for three to four weeks is highly recommended. If using antibiotics, they should be applied ahead of rain events and may be reapplied within one to twodays if EIP value is very high.

Powdery mildew. Diseased apple shoots from buds infected last season are showing up in the region. Powdery mildew was severe in many apple and cherry orchards in 2023 and inoculum levels are high this year. Apples should be protected from secondary infection. Tarts should be treated starting at first cover. If infected shoots are spotted, we recommend pruning them out of the orchard to decrease risk for secondary infections later in season.

American plum borer. An average of 17 American plum borer were caught this week at the Northwest Michigan Horticulture Research Center.

Codling moth. Codling moth numbers increased this week with an average of 33 per trap. The biofix for codling moth in northwest Michigan is May 17. The window for ovicidal treatments (100 GDD base 50 F after biofix) occurred on May 24. The best timing for larvicidal treatments (250 GDD base 50 F after biofix) is predicted to occur in over a week. The current prediction for May 3 at the Northwest Michigan Horticulture Research Center weather station is 212 GDD base 50 after the biofix.

Green fruitworm. Zero green fruitworm were trapped at the Northwest Michigan Horticulture Research Center.

Obliquebanded leafroller. Obliquebanded leafroller larva damage was observed in apples and tarts this week at the Northwest Michigan Horticulture Research Center.

Oriental fruit moth. Zero oriental fruit moth were caught this week at the Northwest Michigan Horticulture Research Center.

Plum curculio. Plum curculio damage on tart cherries has been observed at the Northwest Michigan Horticulture Research Center. Plum curculio will continue to be active this week and apples and cherries are susceptible to damage.

San Jose scale. A total of two San Jose scale male flyers were trapped this week. This year’s biofix is May 18. Crawler emergence is predicted for 400-450 GDD base 51 after biofix. We have accumulated 117.7 GDD base 51 so far.

Spotted tentiform leafminer. Spotted tentiform leafminer numbers have decreased with an average of 16 spotted tentiform leafminer per trap at the Northwest Michigan Horticulture Research Center.


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