Northwest Michigan fruit update – June 4, 2024
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EmailThe northwest region has received ample rainfall, resulting in fast tree and fruit growth. The wet weather and humidity could challenge disease management programs this season.
Weather report
The weather has been variable in the past week. We have had some warm days—on June 3, the maximum temperature was 80.9 degrees Fahrenheit—and cooler days—on May 27, the maximum temperature was 57.9 F. Overnight temperatures have hovered in the mid-50s for the past week. We have also had ample rainfall. The Enviroweather station at the Northwest Michigan Horticulture Research Center recorded 0.21 inch of rain on May 25, 1.19 inches of rain on May 29 and 0.13 inch of rain on June 1 and 3. There is more rain in the forecast for tomorrow, June 5, with potential for thunderstorms. Today, conditions are humid (74% humidity), and the forecast is predicting consistent humidity throughout the week (70%-plus for all days through June 10). These conditions will be a challenge for disease control programs.
Jeff Andresen is predicting that it will be warm and humid today but will cool down by Friday and into the weekend. Daytime highs will drop from the 80s into the 60s, and we may see overnight lows into the 40s and 50s over the weekend. The medium range forecast is calling for cooler than normal temperatures, but by mid-June, we are expected to see warmer than normal conditions return.
So far this season, we have accumulated 863.6 growing degree-days (GDD) base 42 and 430.30 GDD base 50. We are still well ahead of our long-term average: 691.1 GDD base 42 and 358.3 GDD base 50.
Crop report
The following growth stages were evaluated at the Northwest Michigan Horticulture Research Center yesterday morning, June 3:
- Balaton – 12 millimeters (mm)
- Bartlett Pear – 11 mm
- Montmorency – 12 mm
- Potomac Pear – 17.5 mm
- Emperor Francis – 14 mm
- Gold – 11 mm
- Ulster – 14 mm
- Riesling – 10-16 inch shoots
- Gala – 15.5 mm
- Honeycrisp – 17 mm
In most orchards, apples have moved past the optimal time to chemically thin fruit, and apples will be harder to thin at larger size. Accede is a newer material shown to be effective when fruit size is larger, and some growers are trying to make reapplication decisions about thinning. There is a sizeable crop out there, and growers should try their best to thin for optimal fruit quality.
Overall, all tree fruit crops look good in northwest Michigan. There are some sites that were damaged by earlier spring cold temperatures, and there is some variability of crop size in orchards. At the Northwest Michigan Horticulture Research Center, our crop looks good, and fruit is sizing quickly with adequate moisture.
Pest report
Apple Scab. The number of ascospores caught during recent wetting events has been decreasing in southwest, Grand Rapids and west central regions. Primary scab season continues for the northwest region and secondary infection season has begun with the arrival of leaf lesions. The Northwest Michigan Horticulture Research Center had a moderate risk wetting event May 1- 2 on the Enviroweather apple scab model.
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Bacterial canker. Leaf and fruit lesions on sweet cherries from bacterial canker are present in orchards around the region. These fruit lesions may be colonized by the American brown rot pathogen and result in higher fruit rot disease pressure preharvest, especially if the weather remains warm and wet this season.
Cherry leaf spot. Lesions from primary infection are showing up on tart leaves; this is going to be a long season for managing cherry leaf spot disease. The weather this season continues to favor cherry leaf spot development and if unmanaged, disease pressure could become extremely high by the end of the season. Tarts and sweets should be protected.
Fire blight. Shoots inoculated with fire blight bacteria a few weeks ago for a research project at the Northwest Michigan Horticulture Research Center are beginning to ooze and show symptoms of necrosis and flagging. 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 two days if the epiphytic infection potential (EIP) value is very high.
Powdery mildew. Apple shoots infected with powdery mildew have been reported in all counties of the northwest region. Sporulation was observed this week and can result in secondary infection. Symptoms have not been observed yet on tarts. Apples and tarts need to be protected to avoid high disease pressure later in the season. Tarts should be treated starting at first cover. Michigan State University Extension recommends pruning out and removing infected shoots from orchards.
American plum borer. An average of 1.3 American plum borer were caught this week at the Northwest Michigan Horticulture Research Center.
Black stem borer. An average of 6.5 black stem borer were caught this week at the Northwest Michigan Horticulture Research Center.
Codling moth. An average of 12.3 codling moths were trapped this week. The biofix for codling moth in northwest Michigan is May 17. The window for ovicidal treatments at the Northwest Michigan Horticulture Research Center (100 GDD base 50 F after biofix) occurred on May 24. The window for larvicidal treatments (250 GDD base 50 F after biofix) for the Northwest Michigan Horticulture Research Center, Williamsburg, Benzonia and Elk Rapids Enviroweather stations is predicted to occur June 5 and East Leland June 6. Old Mission and Onekama/Bear Lake are predicted for June 8. The prediction for the Northport Enviroweather station is beyond June 10.
Greater peachtree borer. Zero have been caught at the Northwest Michigan Horticulture Research Center. Mating disruption is recommended in orchards with at least five acres and trees that are at least three years old.
Green fruitworm. Zero were trapped at the Northwest Michigan Horticulture Research Center.
Lesser peachtree borer. An average of 7.3 lesser peachtree borer were trapped at the Northwest Michigan Horticulture Research Center.
Obliquebanded leafroller. The biofix (first generation adult emergence) for obliquebanded leafroller at the Northwest Michigan Horticulture Research Center is predicted for June 6. No obliquebanded leafroller adults have been caught thus far.
Oriental fruit moth. Zero oriental fruit moth were caught this week at the Northwest Michigan Horticulture Research Center.
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.
Rosy apple aphid. Damage was observed this week at the Northwest Michigan Horticulture Research Center.
San Jose Scale. An average of 4.3 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 193.9 GDD base 51 so far.
Spotted tentiform leafminer. Numbers have decreased with an average of 1.3 spotted tentiform leafminer per trap at the Northwest Michigan Horticulture Research Center.
