Tree Fruit Newsletter — May 6, 2025
In this newsletter:
- Bud stages at Highmoor Farm
- Brown Rot Blossom Blight of Stone Fruit
- Prohexadione and aggravation of bitter pit in Honeycrisp
- Thinning Peaches with Acceede SG®
Flower Bud Development
Flower bud development has been, thankfully, slow this spring. Honeycrisp apples are still at half-inch green. McIntosh and Gala are just starting tight cluster.
Pears are at the tight cluster stage. Asian pear buds are more advanced than European pears.
Apricots are in full bloom, but with few wild pollinators. There was no sign of brown rot blossom blight.
Peaches are at the red bud stage with the early varieties just starting to show some pink. Buds that are not swelling at this time are dead, probably from winter kill.
Sweet cherries have not yet reached the white bud stage, but a few of the clusters are showing a little bit of white.
Sour cherries are between tight cluster and open cluster stage.
Asian plums are at white bud or in full bloom depending on the variety. I saw enough wild pollinators working the blossoms today.
European plums are not yet at white bud, and most trees have only a scant amount of flowers, for reasons that I don’t understand. I also saw a number of black knot infections that should have been removed during dormant pruning. There is still time to get these out of the orchard before they spread spores to new shoots. Prune back to 8 inches below the infection and remove pruned shoots from the orchard.
Brown Rot in Stone Fruit Trees
At the full bloom stage, the flowers of stone fruit are susceptible to infection by the fungus that causes brown rot, but wet weather is also necessary for infection. Apricots and cherries are the most susceptible. Asian plums and peaches blossoms are not commonly affected at the bloom stage.
I am finding numerous peach mummies from last year’s infected fruit that were not removed during pruning. These can serve as a source of inoculum for spreading the disease this spring. Fungicides just prior to and during bloom will help prevent blossom blight.
The spray table for cherry:
2 – White Bud : New England Tree Fruit Management Guide : UMass Amherst
The spray table for peaches at the pink stage:
2 – Pink : New England Tree Fruit Management Guide : UMass Amherst
Prohexadione and Aggravation of Bitter Pit in Honeycrisp
Prohexadione applied during or after bloom can aggravate bitter pit. This is based on a few years of research at Cornell University. They recommend application at the full pink or late pink stage, for fire blight suppression.
From Cornell Cooperative Extension:
To avoid aggravating BP in Honeycrisp, do not use Apogee or Kudos (prohexadione calcium) for vegetative growth reduction post-bloom as is generally recommended. Our data shows that in 2 years out of 3, “conventional” Prohex use significantly aggravated BP. Contrary to commonly held belief, our data over three years indicates that the reduction of vegetative growth achieved by Prohex is not correlated with a reduction of BP incidence.
Accede SG® for Thinning Peaches
The late pink stage through petal fall is the time when Accede SG® can be applied for thinning peaches and plums. Most of us are reluctant to thin this early because of the chance for frost, or our plantings are too small to justify the use of a chemical thinner for just peaches. For those of you who have larger plantings with very good bud survival, it may be useful for partly reducing the crop load. Here is the link to the product label for Accede: 44-1043R1_Accede SG Domestic_Specimen.indd.
Renae Moran
University of Maine Cooperative Extension: Tree Fruits
PO Box 179
Monmouth, ME 04259
(207) 933-2100
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