West central Michigan tree fruit update – May 27, 2026
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EmailApple trees are at petal fall and early fruit set this week, and stone fruit is out of the shuck in the west central region.
Weather update
Warmer weather over the past few days has rapidly advanced phenology and fruit size across west central and Grand Rapids, Michigan, regions (Figure 1). Wind and rain accompanied the warmer weather over the weekend. Precipitation in Hart was 0.14 inches and in Grand Rapids was 1.13 inches over the past week. Based on the Hart Enviroweather station for May 27, current degree-day (DD) accumulation is 670 DD42 and 340 DD50. At the Sparta Enviroweather station, current DD accumulation is 816 DD42 and 438 DD50.
Weather this week will be hot with high temperatures in the mid-70s and 80s. Nighttime temperatures will stay warmer as well with low temperatures in the low to mid-50s this week in Hart and Sparta. A little rain is in the forecast this week, although there are chances of popup showers on Wednesday, May 27. Windy conditions will continue, and temperatures for the end of May are expected to be warmer than normal with average or below average precipitation.
Listen to the weather update from Jeff Andresen, MSU climatologist, at the Fruit & Nuts Weather page from MSU Extension.
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.
Crop update
With warmer weather over the past few days, tree phenology advanced quickly. We can see initial fruit set and rapidly growing fruitlets in some orchards.
Apple varieties in Oceana County range from petal fall to fruit set. In Hart, early varieties are actively growing. Average fruitlet size for Zestar is 13.4 millimeters (mm), Idared is 15.1 mm and Empire is 11.3 mm. Average fruitlet size for later varieties such as Gala is 9.8 mm, Honeycrisp is 8.2 mm, Jonagold is 11.4 mm and Minneiska is 11.1 mm.
Scout block by block to assess early fruit set to determine potential crop load and thinning needs. There has been a lot of new vegetative growth with the warmer weather with extension shoots and new leaves. At this time, primary spur leaves and bourse shoot leaves are contributing to the sugars going to developing fruitlets. Extension shoots are actively growing, and they start contributing sugars to developing fruitlets about 25-30 days after bloom.
Over the next few weeks, apple thinning sprays will need to be implemented as fruit set can be evaluated. Early thinning strategies can begin for this season with petal fall thinning applications where needed. With the warm weather conditions this week, fruitlets are expected to grow fairly rapidly, around 0.5 mm or more per day. Temperatures this week in the 70s and up to mid-80s will enhance thinner efficacy; however, be sure to check the carbon balance of trees before you apply thinner applications.
Information on the fruit growth rate model and the Malusim carbohydrate model can be found in this article from MSU Extension.
To access the apple carbohydrate thinning model, go to the apple tab in MSU Enviroweather and click where it says “Apple Carbohydrate Thinning.”
For Hart, the carbohydrate thinning model is predicting a carbon deficit (-21.16 g/day for the six-day average on May 27), so use caution if a thinner is applied or wait to apply a thinner until the carbon balance is higher. Warm nighttime temperatures and cloudy daytime conditions lead to high respiration rates which burn carbohydrates and can lead to a carbohydrate deficit. For Sparta, the carbohydrate thinning model is predicting a six-day weighted average of 15.35 g/day, so there is low risk of overthinning. An increased rate of thinner or adding Regulaid is recommended.
See this article on general apple thinning recommendations and decision-making tools. Risk for overthinning at these earlier application timings is low.
Apple scab pressure is continuing, and primary scab spores are still being trapped. According to the RimPro model for Hart, leaf wetting periods have been short which has limited infection periods. Spores were counted at one site in Oceana County from the rain events on May 24 and 25, and 36 spores were counted. The RimPro model predicted spores were ejected during that time and there was an infection event. This was also shown on the Enviroweather model for Hart and surrounding stations. Enviroweather is predicting 99% of the spores are mature and 81% of them have been released. Little to no rain is forecasted for the rest of the week, so no infection risk is predicted at this time for Hart.
Similar conditions are predicted for Sparta. The RimPro model showed an infection period over May 24 and 25, and Enviroweather is predicting 100% of the spores are mature and 92% have been released. Dry conditions this week means risk of infection is low.
The MSU Enviroweather fire blight model for Hart and Sparta is predicting high fire blight infection risk over the next few days due to warm temperatures. EIP values are predicted to be above 71 during May 27–31 in Hart and Sparta, but as bloom finishes up this risk will decrease. If open blooms are present, antibiotic applications are recommended before a rain event to protect blossoms from bacterial infection.
Fire blight is becoming less of a concern in the Grand Rapids region and further south as bloom comes to an end. Start scouting for fire blight symptoms from previous infection events on May 18–19 because symptoms will start to show. Cut out infected tissue as soon as possible because the fire blight pathogen can spread rapidly, as much as 5 centimeters per day in young shoots.
Tart and sweet cherry fruitlets are growing rapidly in Hart. Average fruitlet size is 14.2 mm for sweet cherries and 10.3 mm for tart cherries. If dry conditions persist this week, there is a low risk for cherry leaf spot in tart cherries. There was a light leaf spot infection over the weekend on May 24–25 due to warmer temperatures, rainfall and extended wetting hours.
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. According to George Sundin, MSU tree fruit pathologist, 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.
Peaches are out of the shuck for some varieties. Average fruit size for Venture peach at the West Central Michigan Research and Extension Center in Hart is 7.5 mm. Rusty spot (powdery mildew) and bacterial spot management may be needed in peaches, particularly if disease pressure was high in 2025. For the MSU trapline, oriental fruit moth were trapped this week at the West Central Michigan Research and Extension Center with two per trap. A biofix date has been set for Hart for May 11.
Plum fruitlets are growing rapidly in west central. If needed, management for black knot is recommended. Average fruitlet size for Castleton plums is 13.4 mm.
Pear fruitlets are also growing, and average fruitlet size of Bartlett pear at the West Central Michigan Research and Extension Center is 10.3 mm. Similar to last week, applications to manage pear scab are needed to cover new green tissue similar to apple scab. Pears will also need to be protected against fire blight if there is still open bloom; however, bloom has finished in most varieties in the west central region. Pear psylla adults have been observed in the Bartlett pear block at the West Central Michigan Research and Extension Center.
Additional pest and disease information
No green fruitworm adults were trapped this week in Oceana County. Pest activity is continuing this week with the warm weather. Ambrosia beetle adults and aphids were also observed this week on sticky traps and shoot terminals.
Other pests to scout for include obliquebanded leafroller, American plum borer, rose chafer, green peach aphid, European red mite and white apple leafhopper.
For more information about regional reports, please visit the Michigan State University Extension website.
This work is supported by the Crop Protection and Pest Management Program (grant no 2024-70006-43569) from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
