West central Michigan tree fruit update – May 3, 2022

Emily Lavely<lavelyem@msu.edu>, Michigan State University Extension - May 03, 2022

Cool weather has slowed bud development, but changes are still occurring as we inch closer to bloom.

Apple, peach, cherry and pear branches. — Figure 1. Stage of tree phenology for apple, peach, cherry and pear in Oceana County on May 2, 2022. Photo by Emily Lavely, MSU Extension.

Weather update

Cooler weather has slowed bud development, but new growth is still emerging across west central Michigan (Figure 1). Based on the Hart Enviroweather station for May 3, current growing degree day (GDD) accumulation is 187.1 GDD₄₂ and 65.3 GDD₅₀. Across the region, GDD accumulation continues to be below the five-year average (Table 1).

Cool weather will continue through the week with a slight warm up over the weekend. Highs will be in the 50s up to mid-60s with lows in the 40s. Rain showers will occur on Tuesday this week as well as toward the end of the week. Warmer temperatures in the 70s are expected early next week.

Table 1. Current and five-year average GDD summary from Jan. 1- May 3. Numerical integration was used for degree day calculations.
Station	2022 GDD base 42 F	5-year average GDD base 42 F	2022 GDD base 50 F	5-year average GDD base 50 F
Benona/Shelby	149	193.7	48	66.8
Elbridge/Hart	174	243.5	63	95.8
Fremont	193	277.5	72	112.7
Grant*	210	266.1	82	109.1
Hart	179	238.7	64	92.7
Ludington	171	226.5	61	85.2
Mears**	183	260.6	65	98.6
New Era**	170	255.4	60	92.5

*Averages were calculated using data from 2020-2021.
**Averages were calculated using data from 2018-2021.

GDD graph — Figure 2. Cumulative and forecasted degree days for base 42 F and base 50 F for the Hart Enviroweather station.

Weather data was gathered from MSU 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.

Crop update

Growers have been able to get out into the field to finish tree trimming, clean up brush, plant trees, and install trellis systems where needed. For some growers, protective sprays were also applied to protect new green tissue that emerged over the weekend from scab and fire blight.

With cooler temperatures this week, further growth is expected to be slow. A warmup early next week could advance growth rapidly.

Apple varieties in the west central region range from green tip to tight cluster. Early varieties such as Zestar and Idared are close to tight cluster. Later varieties such as Gala and Honeycrisp are at half-inch green with some late varieties, like Northern Spy, at green tip. As a reminder, half-inch green in apple averages 205 GDD₄₂ for McIntosh based on over 30 years of observation from Sparta, Michigan; other apple varieties will be ahead or behind McIntosh. Hart is at 187.1 GDD₄₂and 65.3 GDD₅₀. There appears to be a high number of fruit buds in 2022, and growers are advised to start thinking about their thinning program early this year. For more information on thinning strategies for Honeycrisp in 2022, check out this article from Michigan State University Extension specialist Anna Wallis, “Honeycrisp crop management for 2022.”

Cherry buds range from side green to green tip. Tart cherry buds are moving slowly but are generally at green tip across the region. Early sweet cherry varieties are at tight cluster. There may still be time to apply delayed dormant sprays to manage bacterial canker and early pests such as mites or scale insects. As a reminder, if growers are using oil and copper sprays, these products should be avoided once green tissue is present because they can cause tissue damage (phytotoxicity).

Peaches are in the bud swell to red calyx stages. If growers have not already applied a spray for peach leaf curl, an application for final spring sprays for management of peach leaf curl and bacterial canker is warranted in the next week. Cool wet weather this spring may increase risk of peach leaf curl infection. Ideal infection conditions include 10 or more hours of leaf wetness at a temperature range of 46 – 55 degrees Fahrenheit. It isn’t hard to manage peach leaf curl, but it will be important for growers to keep new tissue protected with the cool, wet conditions this spring to prevent high infection levels.

Pear varieties range from bud scale separation to blossom bud exposure.

Pest and disease update

Insect activity in the west central region has also been slowed by cooler temperatures this spring. Pear psylla eggs were identified on Bartlett pear on Friday, April 22. The insect trapline at Trevor Nichols Research Center (TNRC) captured a few adult green fruitworm this week, but green fruitworm is not a major pest in our area. An average of 10.3 red banded leafroller 114.3 spotted tentiform leafminer were also trapped on May 2 at TNRC. With cool and rainy conditions this week, we expect insect pest activity to continue to be low in west central Michigan.

Emerging tissue in apple remains at low risk for apple scab infection. Generally, our wetting periods have not been long enough to result in infection. Due to cooler forecasted temperatures with highs in the 50s and mid-60s, risk of scab infection is predicted to be low. Once green tissue is present, it needs to be protected with adequate fungicide coverage.

It's time for growers to start thinking about 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 plant pathologist 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 not unfolded yet, so we currently do not expect any risk of infection. However, disease pressure was high in 2021, and maintaining coverage of new tissue will be critical in west central Michigan this season.

Some growers have also 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. There was high fire blight pressure in west central Michigan in 2021, and it will be important for west central Michigan growers to manage fire blight this year, particularly in young, high-density plantings.

For pest and disease management recommendations, please refer to the Michigan 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).