Hello fruit growers, we are excited to share apple and grape scouting updates with you this year through the Wisconsin Fruit Newsletter. Harvest is in full swing for most tree fruit and grape growers. Weather has been variable, with cooler nights as we inch closer to fall. Several secondary insects continue to be observed, including Japanese beetle, aphids and mites. Continue scouting and monitoring.

As a reminder, this newsletter will cover apple and grape phenology, general scouting observations, and includes an overview of degree day accumulation in fruit growing regions. Growers can reference the Midwest Fruit Pest Management guide for further information on pest management best practices.

Grapes

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, all grapes have been harvested as of Friday, September 11. Grapes at PARS are at EL stage 36-37. West Madison had high pressure of wasps and birds. Keep in mind the pre-harvest interval if treating for wasps as we move through harvest.

Below displays the GDD accumulations from April 1 through September 11 for the current and last two seasons. This data is collected using the NEWA website. You can visit their “About degree days” page to learn more about the concept of degree days as well as the formulas utilized for calculations. Continue scouting and keeping an eye on the NEWA models in your area. Degree day accumulation in 2026 has been similar to the past two seasons. 

Growing degree day (GDD) accumulation as of September 11, 2026 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

• Keep an eye out for summer fruit rots. Check out this video for more information on identification and management recommendations here: Distinguishing and Managing Grape Bunch Rots (UW-Madison Extension).
• Overview of grape insect/mite monitoring and management: Grape Insects and Mite Pests, 2024 Field Season (Cornell, 2024).
• Wasp pressure has been high in the last several weeks. Keep in mind pre-harvest intervals if using an insecticide to control wasps.
• With the hot weather, be sure to monitor irrigation needs—especially for newly established vineyards. Without adequate water, young vines may halt growth. If irrigation is available on your farm, use it to support optimal early development, as water is critical for maximizing growth during establishment.
• Growers can reference the NEWA weather station network to monitor for disease infection periods in their area. Check out your nearest weather station: NEWA Weather Station Network (Cornell).
• Grape growers monitoring spotted wing drosophila should continue checking and refreshing traps weekly.
• Grape berry moth has been observed in southern WI. Continue monitoring traps and using NEWA models.
• Sanitation: remove and destroy (chop/compost) fallen fruit ~weekly to prevent any internally developing larvae from reaching maturity, and to limit the spread of disease.
• Check out the WI DATCP Orchard Insect Pest Bulletin for more information on current insect trap captures across the state.

Apples

Apples are continuing to build size and are starting to color up, likely driven by the heat and humidity. Many growers in southern WI are picking honeycrisp, and varieties seem to be slightly early this year likely due to warm temperatures and water stress through the summer. Growers should continue monitoring the NEWA models for summer fruit rots and remember to check labels for pre-harvest intervals.

We are tracking growing degree days (DD 43 °F BE) from January 1 to monitor bud development in apples. This data is collected using the NEWA website. You can visit their “About degree days” page to learn more about the concept of degree days as well as the formulas utilized for calculations. Similar to grapes, degree day accumulation (Base 43°F BE*) between January 1 and September 11 in 2026 is slightly higher compared to the 2024 and 2025 season. Temperatures will shift to be a bit cooler in the next week, with highs in the 70s and lows in the 50s and a chance of rain next week in Southern Wisconsin.

Growing degree day (GDD) accumulation in 2024, 2025 and 2026 as of September 11 (January 1 start date; base 43°F BE*).

*BE = Baskerville-Emin calculation method