Tree Fruit Newsletter — May 22, 2026
In this newsletter:
- Thinning Time
- Announcements
Thinning Time
Apples & Pears
Apple and pear trees were in full bloom this week at Highmoor Farm. We observed plenty of bee activity in apples, pears and stone fruits and may have to thin aggressively in the next few weeks. The combination of heavy return bloom, good pollination and cool temperatures could make it difficult to thin enough this year.
I am not sure if last year’s drought will have any carry-over effect on fruit set and thinning. Based on the strength of return bloom, I plan to proceed with thinning as usual and will consider the daytime high temperatures and the variety as the most important factor in determining timing and thinner rates.
The long-range forecast indicates mostly cool temperatures which means thinners will have less potency. Maxcell and other BA-type thinners are ineffective at temperatures below 70 ºF. The next warm day in the forecast is Tuesday when high temperatures will be favorable for effective thinning.
The Network for Environment and Weather Applications (NEWA) website now has the carbohydrate model for thinning for the Monmouth area which predicts thinning effectiveness based on solar radiation and temperature measured at our new weather station. Once on the NEWA home page, select the Monmouth, ME station and then select the carbohydrate model under IPM & Crop Tools. The model indicates a negative carbohydrate balance in apple trees for May 27 which means better chemical thinning.
Apple trees will be at petal fall soon when most thinners become effective. Here is the link to the chemical thinning tables in the New England Tree Fruit Management Guide: Chemicals for Apple Thinning.
Peaches
Peaches can be bloom-thinned at this time which is much easier than hand thinning fruit later and leads to bigger fruit size. We usually remove 50% to 75% of the blossoms from trees that have good return bloom and survival. On trees that have less flower survival, we remove 10% to 20% leaving about 3 to 4 flowers on each shoot. Some varieties in our collection will not need thinning.
Hand thinning can be delayed on peach trees that were chemically thinned with Accede.
Announcements
Webinar: Wednesday, May 27, 2026
Improve Spray Timing and Reduce Risk with NEWA and Weather Data
2pm – 3pm (America/New York)
Making the right pest and disease management decisions comes down to timing, and getting it wrong can mean wasted inputs, higher costs, and increased crop risk. In this webinar, you’ll learn how growers are using NEWA decision-support models together with on-site weather data to make more precise IPM decisions for spray timing, irrigation, and crop thinning.
Join Jon Clements (UMass Extension) and Matt Sharp (HOBO) as they walk through how NEWA models work in practice and how integrating real-time weather data can help improve the accuracy and effectiveness of your management decisions. This session will include a live demonstration of the NEWA website, where you’ll see how to use IPM tools to support real-time decision-making in the field.
More information and to register: Improve Spray Timing and Reduce Risk with NEWA and Weather Data | Onset’s HOBO Data Loggers
Renae Moran
University of Maine Cooperative Extension: Tree Fruits
PO Box 179
Monmouth, ME 04259
(207) 933-2100
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