Tree Fruit Newsletter — June 3, 2025

In this newsletter:

• Thinning Outlook
• Fruit Set in Different Varieties
• Poor Return Bloom
• Other Observations of No Concern

Thinning Outlook

Good temperatures for chemical thinning will occur this week and into next week. The warm temperatures will mean that fruit can rapidly grow to a size where they become resistant to chemical thinners. Most varieties were about 7 mm on Monday and could grow to 15 mm before the end of next week.

Fruit Set in Different Varieties

Fruit set in various apple orchards was evident at Highmoor Farm on Monday, but also some clusters with fruitlets that were too undeveloped to tell if they will persist or drop. Pears had poor return bloom but good fruit set.

McIntosh apples appear to have set with one to three fruit per cluster at Highmoor Farm, but some clusters that are blanks with no fruit. This variety had more blanks than other varieties. My assessment indicates a need for some thinning to break up clusters. With the warm temperatures predicted, I am suggesting a mild thinning strategy for this variety. King fruit diameter was 7 mm on Monday. Some McIntosh trees have sparse bloom. When fruit set is very light, trees are less responsive to chemical thinners.

Honeycrisp has good fruit set in the more advanced clusters, but most clusters were not yet at the stage where the extent of fruit set could be seen. Fruit diameter ranged from 5 to 8 mm.

Cortland fruit set appears to be good with about four fruit per cluster and very few blanks. Fruit diameter was 8 mm on the early blooming clusters and 5 mm on the later blooming ones. Response to thinners in this variety takes a long time, so it may appear that chemical thinners have worked until after the thinning window.

Macoun has mixed fruit set meaning there are some blanks and some clusters set heavy with four fruit. This means thinning is needed with a moderate to aggressive rate of thinning depending on your orchard and the need for large fruit size. Macoun is known to grow small apples. Fruit diameter was 7 mm.

Evercrisp is reported to be self-thinning, meaning that chemical thinning is generally not needed.

Ambrosia had some clusters that were net yet in full bloom. This means they are at risk of fireblight during the next infection period this Thurs.

Gala, Fuji and Golden Delicious fruitlets were not yet at a stage where fruit set could be seen. Fruit diameter was 6 mm.

Triumph had good fruit set with three to four flowers per cluster. Fruit diameter was 10 mm. Some trees have very few flowers. These trees are interplanted with other varieties and will get the thinner mix of the dominant variety in our orchards which is now Honeycrisp.

Poor Return Bloom

We have noticed poor return bloom in some of our orchard blocks at Highmoor Farm. A few growers in the state have also reported this. My best guess for what has caused poor return bloom is the very dry period of weather during and after harvest last year. This time coincides with flower initiation within the terminal buds. Flowers begin to form in summer with additional flower bud initiation through the fall. Any stress during this period can prevent flower development and result in poor return bloom.

If you have seen this in your orchard, make a record of it for each block if you have crop insurance. You can also contact your insurance agent to let them know that it has occurred and can contact me if you need additional documentation. I can make site visits to observe the severity and to help with knowing why particular blocks may have low yield this year.

Other Observations of No Concern

Powdery mildew infections have shown up in Honeycrisp trees but are few and far between at this point in time. Curled foliage on shoot tips indicates a possible powdery mildew infection. It is normally not severe enough to justify spraying, and hopefully that is the case this year.

Aphids have been noted in peaches. They have some resemblance to peach leaf curl, but with closer observation, aphid bodies or their remains can be seen on the undersides of curled foliage. This should not be a concern or reason to spray since they rarely cause any stress to the tree or damage to fruits.

Renae Moran

University of Maine Cooperative Extension: Tree Fruits

PO Box 179

Monmouth, ME 04259

(207) 933-2100

rmoran@maine.edu

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