May 16, 2024

By Becky Wiepz and Dan Kielar

Cool sunny days are causing bloom to last longer and the interspersed sunny days should result in good pollination based on the number of bees we’re seeing in the PARS orchards.

Insect pressure appears to be high, likely due to the mild winter while continuing rain events have led to an increase in fungal pressure and fewer opportunities for cover sprays.

Date 5/152020202120222023202420-year avg.
Base 5073.5144147174.5226159
GDD50 continues to be approximately 7-10 days ahead of the 20-year average.


Most trees have entered bloom, between king and full depending on the variety. The window for bloom thinning will be complete soon and the use of hormonal thinners like NAA and MaxCell will be necessary while fruitlets are still small.

To review or learn more about options for thinning, visit any of the following articles from the UW Fruit Program:


PROTECT POLLINATORS – Do not spray insecticide during bloom!

Blossom feeders including Pug Moths and other Lepidoptera species have been found in some blocks, and a heavy Green Fruit Worm and Spotted Tentiform Leafminer flight continue.

Some Oblique- and Red-Banded Leafrollers have been caught, signaling the start of their emergence.

Codling Moths have not been caught in any blocks yet.


Apple Scab pressure continues to be high as spore release is ongoing and wetting events are regularly occuring. Full cover sprays are needed on tight windows to protect new growth.

Despite our prolonged bloom, fireblight risk has remained low due to the cool temperatures. Nevertheless, plans and products should be in place so a quick response can be achieved if risk levels increase.

Fireblight risk is ‘High’ when the following conditions are met:

  • A certain number of heat units must accumulate during bloom for a threshold level of inoculum to be reached;
  • a wetting event is necessary after this point to wash the bacteria to their infection sites; and
  • the average temperature is above 60F

You can gauge fireblight risk at your orchard using the NEWA Fireblight Model.

To learn more about the apple scab and fireblight models from NEWA, visit the ‘Newsletters’ section of the Cornell Tree and Small Fruit Extension Resource Blog.


Most orchards are in full bloom to early petal fall.


There is no concern for insect pests in cherries right now. Scout for Plum Curculio after the cherries are out of the shuck.


Cherry leaf spot pressure is low based on the predictive models but continued wet weather means protective cover sprays should go out ahead of rains. Monitor your local Cherry Leaf Spot risk by visiting the ‘Wisconet Crop Models’ link from your nearest weather station at


Grapes on the station are at budburst. The first fungicide application of the season should occur before shoots reach 3 inches of growth.