MSU Extension Fruit & Nuts

Weather update

Warm weather has advanced flower bud development in tart cherry, pear and apple across the west central and Grand Rapids, Michigan, regions. Sweet cherry, plum and some peach varieties are in early petal fall. Warmer daytime temperatures in the west central region means there is a lot of new leaf growth and opening flowers. In early apple varieties, such as Zestar and Idared, trees are in full bloom in the Hart area. Honeycrisp, SweeTango and Jonagold are in early bloom. Based on the Hart Enviroweather station for May 12, current degree day (DD) accumulation is 410 DD₄₂ and 181 DD₅₀. For the Sparta Enviroweather station, current DD accumulation is 539 DD₄₂ and 267 DD₅₀.

Degree day accumulation is variable compared to the five-year average for the west central region (Table 1) with some sites being ahead, similar or behind the five-year average. The Grand Rapids region is slightly ahead of the five-year average (Table 2) according to the Michigan State University (MSU) Enviroweather stations.

For the next few days, it will be hot across the region. In Hart and Sparta, temperatures are forecasted to have highs in the upper 70s and low to mid 80s with warm overnight temperatures. Temperatures will cool down slightly toward the end of this week and into next week with highs in the 60s and lows in the upper 40s and low 50s. Chances of rain and thunderstorms are predicted for every day this week, especially Tuesday through Thursday. However, the amount of rain in the forecast is low, and soil conditions are very dry.

Get the full weather update from Jeff Andresen, MSU climatologist.

Table 1. West central region: Current and 5-year average DD summary from Jan. 1- May 12. Numerical integration was used for degree day calculations.

Table 2. Grand Rapids region: Current and 5-year average DD summary from Jan. 1- May 12. Numerical integration was used for degree day calculations.

 Weather data was gathered from MSU Enviroweather.

Soil moisture is low for the Hart Enviroweather station as of May 12. Maximum soil temperature at 2 inches depth was 71.6 degrees Fahrenheit, and at 4 inches depth the maximum temperature was 66.6 F. Maximum soil moisture at 4 inches is only 7% and at 20 inches it is 7.7%. This means that a large portion of the root zone is very dry. For the Sparta Enviroweather station on May 12, maximum soil temperature at 2 inches depth was 82.6 F, and at 4 inches depth the maximum temperature was 75.2 F. Maximum soil moisture at 0-12 inches is 38.6% and at 20 inches it is 53.4%.

Irrigation may be needed this week, especially for young trees and high-density plantings, particularly in sandy soils. Ground cover and higher soil moisture content from rain or irrigation help keep soils cooler, which could enhance root and soil microbial activity in the soil. Information and recommendations for irrigation can be found at: 

• Apple Irrigation Model | NEWA (cornell.edu) 
• Drip Irrigation for Tree Fruit Orchards in Pennsylvania (psu.edu) 

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.

This has been great weather for pollination. Here are some general reminders to protect pollinators from an article written by Jackie Perkins and Ana Heck from Michigan State University Extension.

The best way to protect pollinators from pesticide exposure is to avoid sprays while crop flowers are open. However, pest and disease pressure may warrant applications during bloom. Follow these guidelines whenever possible to protect pollinators: 

• Use pest scouting, weather tracking, development models, etc. to determine if/when sprays are necessary and reduce unnecessary applications. 
• Where possible, use integrated pest management strategies such as biological, cultural or mechanical control in place of pesticide applications. 
• Make applications when bees are not flying (after sunset or before sunrise, when air temperature is below 50 F).
• Consider using liquid formulations when available, as powders and encapsulated pesticides are more likely to be picked up by foraging bees.
• Use drift reduction practices such as nozzle calibration, targeted spraying and monitoring wind speeds.
• Remove flowering weeds from within crop rows if the flowers are likely to be exposed to pesticide drift (e.g., dandelions and clovers). 
• Maintain good communication with your beekeeper if renting hives and consider developing a pollination contract. 

Crop update

Apple varieties in Oceana County range from early bloom to full bloom. Early varieties such as Zestar and Idared are at full bloom and will likely be starting petal fall by the end of the week. Later varieties such as Gala and Honeycrisp are at first bloom. In the Grand Rapids area, varieties such as Smitten and Red Delicious are in bloom, and Honeycrisp are in early bloom.

Sweet cherry are at petal fall for some early varieties, and tart cherry are about in full bloom in Oceana and Mason counties. For tart cherry, bract leaves have emerged, and tissue is susceptible to cherry leaf spot. When the bract leaves emerge, stomates are mature enough for infection.

Peaches are at full bloom or petal fall depending on the variety. Venture peach at the West Central Michigan Research and Extension Center are at petal fall.

Apricots are in the shuck in Oceana County, and fruit that set are growing steadily.

Plums are at full bloom or petal fall for European and Japanese varieties.

Pear varieties are at full bloom or early petal fall for Bartlett pear at the West Central Michigan Research and Extension Center.

Early thinning strategies can also be implemented at bloom and petal fall for apple and peach. Options for apple thinning at various timings can be found in the MSU Apple Thinning Guide. At bloom time, products like Lime Sulphur (2%) plus Oil (2%), ATS (2-2.5%), Amid-Thin and NAA can be used for mild thinning. At petal fall, products such as carbaryl and Amid-Thin can be used as mild thinners. These products at early timing support the nibble thinning approach to manage crop load in apple.

Pest and disease update

General fungicide application reminders. The weather forecast has been highly variable this spring with periods of cool and warm weather. Rainfall has also been highly variable across the state. In the west central and Grand Rapids regions, little rainfall has occurred over the past few weeks. With extended bloom and new leaves growing, there are a few things to consider.

Optimal disease conditions for American brown rot in stone fruit are warm and wet weather with temperatures between 70-80 F. Although the bloom period has been extended, it has been so dry that one brown rot spray is likely sufficient unless you had high disease pressure from last season. If you have not applied a brown rot spray yet this year for stone fruit, an application may be needed before petal fall.

Optimal conditions for apple scab and cherry leaf spot are wet and warm conditions. With warmer average daily temperatures, fungi require less time to grow and initiate infection compared to cool temperatures. With the small amounts of rain in the forecast, consider if another fungicide application is needed. For example, if the previous spray was seven to 14 days ago, another protective spray may be needed to cover new and existing tissue. However, if a fungicide was applied more recently, fungicide residue should still be present. A general rule of thumb that is often used is that 1 inch of rain removes about 50% of the protectant fungicide residue, and over 2 inches or rain will remove most of the spray residue. 

For fire blight, the flower is the critical site for multiplication of the bacterial Erwinia amylovora. Warm temperatures, particularly in the 70s to low 80s, are optimal for bacterial growth. These bacteria do not need rain to grow on the stigma; however, they do need free moisture. As little as 0.01-inch rain can move bacteria from the stigma tip down the outside of the style to the base of the flower where infection occurs through the nectaries. If EIP values are above 70, antibiotics are needed to manage the fire blight bacteria during bloom. When the EIP is high (above 200) and rain events are forecasted, the application of streptomycin or Kasumin would be best about 24 hours before the rain event. A second application may be needed about one to two days after the rain event. If bloom is extended, additional applications should depend on current and future conditions. For example, if temperatures cool significantly and EIPs are reduced to low to moderate risk values (less than 70), sprays can be held off. If EIPs remain high, a third application should be made within two to four days based on the occurrence of wet or dry conditions if blossoms are still open.

West central area

Diseases. With hot temperatures over the past few days, leaf growth and flowers changed rapidly in apple, and this tissue is at risk for primary apple scab infection. There is a slight chance of thunderstorms or rain from May 13-17. Infection periods may be light depending on the rainfall amounts.

The powdery mildew fungus grows well in warm and humid conditions. Powdery mildew does not need wet conditions to infect leaf tissue like apple scab does.

With apple and pear in bloom, warm temperatures, and rain in the forecast, there is risk of fire blight this week. Watch the fire blight model through Enviroweather (Maryblight) for fire blight risk at your nearest Enviroweather station. The fire blight pathogen grows well at temperatures over 65 F, and the fire blight model uses 65 F as a based temperature to calculate degree hours for infection risk. Other factors that are included in the model are if the trees are in bloom and wetting events (rain, dew, fog or spraying). To review some helpful reminders about fire blight management, check out “A primer for Streptomycin, Kasumin and Oxytetracycline use for fire blight management” from George Sundin, MSU tree fruit pathologist.

Insect pests. In Oceana County, no green fruitworm were trapped this week. Fewer redbanded leafroller (11 adults per trap) were trapped this week. Black stem borer were trapped this week in Oceana and Mason counties. Sustained catch of oriental fruit moth occurred this week with an average of 37 moths per trap, so a biofix date has been set for May 5. Monitor orchard blocks closely to set block specific biofix dates where needed. No codling moth, lesser apple worm, American plum borer or dogwood borer were trapped this week in Oceana County.

Codling moth were trapped for the first time this week in Fennville, Michigan, at the Trevor Nichols Research Center and in Sparta, Michigan.

Grand Rapids area

Information provided by Amy Irish-Brown, Valent USA, on May 13, 2025.

Tree fruit diseases. Rain events have been variable across the general Grand Rapids region in the last week, some getting rain, others no rain.

The biggest concern is fire blight in open bloom. The MaryBlyt model is calling for infection on all apples with open bloom, not just the cultivars we know are highly susceptible. The warm, light rain overnight led to foggy conditions through the morning – perfect conditions for blossom blight. The risk remains very high for the rest of this week until cooler temperatures move back Monday and Tuesday and petal fall takes place. Apple tissue is very tender and shoot blight is also of concern with current conditions. Keep any eye on the potential stormy conditions forecasted for Thursday into Friday, May 15-16.

I track apple scab ascospore release near the Sparta Enviroweather station. Rain overnight on May 12-13 discharged only 72 spores on average. All the rain was in nighttime hours and that most likely accounts for the lesser number of spores with this event. The Sparta Enviroweather station rain event was 1 hour shy of being a light infection. With all the tender foliage and tiny, fuzzy fruits present, it’s the right time to keep fungicide cover sprays adequate and use systemic materials to give that added protection. I expect primary scab to continue into the first week or two of June before all spores are discharged.

The higher humidity and warmer temperatures this week will crank up powdery mildew. Make sure you have materials that work on mildew in the tank too.

Tree fruit insects. The warmer weather is waking up many insect species. There seems to be a higher level of obliquebanded leafroller larvae that last spring. Target this pest right now with DiPel to curb the summer generation, which is harder to manage. Petal fall applications may need to happen sooner rather than later this year to stay ahead of insects such as plum curculio that will be active in this warmer weather. Make sure your, and your neighbor’s, bees are removed before you apply insecticides near property lines.

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.