May 9, 2024

By Becky Wiepz and Dan Kielar

Welcome back to PARS pest updates for 2024!

Warming spring temperatures have pushed bloom ahead of schedule throughout the state with most Tart Cherry blocks at or near full bloom. In Door County, apples range between pink and king bloom depending on the variety while grapes are at bud swell.

The continuing rain events mean an increase in fungal pressure and fewer opportunities for cover sprays.

Date 5/82020202120222023202420-year avg.
Base 505911257.5108182.5122
GDD50 is approximately 7-10 days ahead of the 20-year average.


Trees moved from dormancy to half-inch green quickly due to early warm weather and are now hesitating around the pink stage due to the cooler temperatures.

Despite the stagnation in development it’s important to have your thinning plans in place now, particularly if you plan to bloom thin, as progression can move quickly once heat arrives.

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!

Green fruit worm flight peaked the last week of April and is now waning as Spotted Tentiform Leafminers and Oblique- and Red-Banded Leafrollers’ flight has started.

While no codling moths have been caught, an early flight is expected due to the warm weather and mild winter.

Be sure to scout your orchard for Pug Moths and other Lepidoptera species as they can feed on and in blossoms.


Primary Apple Scab spore release is ongoing and full cover sprays are needed on tight windows to protect new growth.

As we go into bloom, fireblight protection is critical to prevent blossom infection. Plans and products should be in place so a quick response can be achieved if conditions enter the ‘High Risk’ category.

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.


In the Sturgeon Bay area, most orchards are approaching full bloom with orchards throughout the county at least at tight cluster. Bud damage from the late April freeze ranged from 12% to 51% loss, but yields shouldn’t be negatively affected if the weather remains clear for pollination.


There is no concern for insect pests in cherries until shuck split exposes fruitlets to Plum Curculio.


Cherry leaf spot pressure is present with the recent rain events if bract leaves are exposed in your orchard. 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 just at budswell. Pruning should be complete before shoot growth starts.