West central Michigan tree fruit update – May 2, 2023

Emily Lavely<lavelyem@msu.edu>, Michigan State University Extension - May 02, 2023

Cool temperatures slowed bud development over the past week as we inch closer to bloom. Sweet cherries and early peaches are in full bloom in some orchards in West Central.

Stage of tree phenology for apple, peach, cherry, plum and pear — Figure 1. Stage of tree phenology for cherry, apple, peach, apricot and pear in Oceana County on May 1, 2023. Photo by Emily Lavely, MSU Extension.

Weather update

This week, we’ve had cooler temperatures than normal with rain and snow in the mix. Bud development has continued to be slow with cool temperatures this past week in west central Michigan (Figure 1). Below-freezing overnight temperatures were observed across the region last week. In some areas, overnight temperatures ranged from 24-28 degrees Fahrenheit on April 25. Based on the Hart weather station for May 2, current growing degree day (GDD) accumulation is 228 GDD₄₂ and 114 GDD₅₀. Across the region, GDD accumulation is slightly above the five-year average (Table 1).

Cool weather and potential for snow is forecasted over the next few days with a warmup going into the weekend. The warmup this week could advance growth rapidly. Over the weekend, highs will be in the 60s F and 70s F with lows in the 40s F and 50s F.

Table 1. Current and five-year average GDD summary from March 1- May 2. Numerical integration was used for degree day calculations.
Station	2023 GDD base 42 F	5-yr avg GDD base 42 F	2023 GDD base 50 F	5-yr avg GDD base 50 F
Benona/Shelby	197	160	94	55
Elbridge/Hart	222	195	112	76
Fremont	233	221	110	88
Grant	246	233	120	96
Hart	228	190	114	72
Ludington	220	182	112	69
Mears	224	224	112	83
New Era	211	210	102	76

Weather data was gathered from Enviroweather.

More information and reports on normal weather conditions and departures from normal can be found on the NOAA Climate Prediction Center website, NOAA U.S. Climate Normals website, NOAA Climate Normals Quick Access Page (which may be searched by region) and Midwest Regional Climate Center website.

Watch the full weather outlook from MSU meteorologist Jeff Andresen.

Crop update

Apple varieties in the west central region range from tight cluster to pink. Early varieties such as Zestar and Idared are at pink. Later varieties such as Gala, Honeycrisp and Minneiska are at open cluster or first pink. With bloom rapidly approaching, start thinking about your thinning program early this year. For general information on thinning strategies for Honeycrisp, check out this Michigan State University Extension article, “Honeycrisp crop management for 2022.”

Cherry buds range from open cluster to full bloom. Tart cherry buds are moving slowly but are generally at open cluster or first bloom, and bract leaves are emerging. Early sweet cherry varieties are at full bloom. To increase fruit set in sweet cherries, growers can use ReTain, a plant growth regulator that has been shown to increase fruit set and yield. Based on experiments at the Northwest Michigan Horticultural Research Center, MSU Extension recommends making ReTain applications early: popcorn to first bloom. Slow drying conditions are preferred. More information on ReTain experiments in sweet cherry can be found in “ReTain use to increase sweet cherry yields” from MSU Extension.

Peaches are at pink to full bloom for early varieties. Growers can begin thinning fruit at bloom. Potential blossom thinning options include dragging large diameter ropes across canopies, rubbing buds with a gloved hand or brush, and spraying canopies with high pressure water systems. Chemical methods using caustic blossom thinners such as ammonium thiosulfate (ATS) are effective, and they damage flower parts and prevent pollination. Using ACC as a bloom thinner may also be a viable option in the future. Formulations of ACC are not widely available for growers at this time and are under evaluation, but preliminary results suggest that ACC could be an effective chemical thinner for peaches. More information on peach thinning strategies can be found in “Thinking through strategies for peach crop thinning” from MSU Extension.

Pear varieties range from tight cluster to first white. Bud stage for the variety Gem was more advanced and at first white in Oceana County compared to Bartlett or Cold Snap.

Pest and disease update

Insect activity in the west central region has also been slowed by cooler temperatures this spring. Pear psylla eggs and adults have been observed on Bartlett pear at the West Central Michigan Research and Extension Center. The insect trapline at Trevor Nichols Research Center (TNRC) did not catch any adult green fruitworm this week. An average of 64 red banded leafroller and 595.7 spotted tentiform leafminer were also trapped on May 1 at TNRC.

With cool and rainy conditions this week, we expect insect pest activity to continue to be low in west central. Only three green fruitworm were trapped this week in Oceana County on May 1.

Apple scab: Emerging tissue in apple remains at low risk for apple scab infection. Generally, temperatures have been so cool that wetting periods have only led to low infection risks. Due to cooler forecasted temperatures with highs in the 40s F and 50s F and low spore counts, risk of scab infection is predicted to be low to medium. Once new green tissue is present, protective sprays should be applied with adequate fungicide coverage.

Cherry leaf spot: It's time for growers to begin cherry leaf spot management. Cherry leaf spot is caused by the fungus Blumeriella jaapii. This fungus overwinters on the ground in diseased leaves. Fungal ascospores are released in spring during prolonged wetting events. In 2020, MSU’s George Sundin reported that spores can infect as soon as bract leaves emerge. Spores infect through open stomata, and stomates on bract leaves were shown to be open when they emerged from buds. Bract leaves are beginning to unfold, so providing coverage of new tissue will be critical moving forward this season. Risk of infection is still low due to cooler temperatures. For example, at 50 F, it takes 19 hours of a wetting period to get infection.

Fire blight: Some growers have applied copper in apple and pear to knock down bacterial populations of the fire blight pathogen, Erwinia amylovora. Dormant and delayed dormant sprays help management fire blight primarily if fire blight was present the previous season. Early apple varieties are at pink and may be in bloom this weekend or early next week. Once flowers open, begin managing for blossom blight.

For pest and disease management recommendations, please refer to Fruit Management Guide (E-154) for product guidelines.

For more information about regional reports, please visit the Michigan State University Extension website.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).