Hello fruit growers, we are excited to share apple and grape scouting updates with you this year through the Wisconsin Fruit Newsletter. Weather has cooled slightly and rain has slowed down considerably in the past two weeks. Table grape variety trials were partially harvested this week at WMARS with remaining varieties to be picked in the next ~two weeks. As a reminder, this newsletter will cover apple and grape phenology, general scouting observations, and includes an overview of degree day accumulation. Growers can reference the Midwest Fruit Pest Management guide for further information on pest management best practices, including recommended chemical best practices. 

Grapes

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, fruit average around E-L* stage 36 (Berries with intermediate sugar values) on Petite Pearl and La Crescent to E-L stage 37 (Berries with intermediate sugar values) in Brianna, Frontenac and Marquette. 

*E-L stands for Eichhorn-Lorenz growth stages scale to describe grapevine development. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through August 27 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.

Growing degree day (GDD) accumulation as of August 27 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

Note: The Sturgeon Bay NEWA weatherstation is out of service and is not included in this report.

Location	2025	2024	2023
Verona WMARS	2234	2240	2317

*BE = Baskerville-Emin calculation method

Maturity Testing – Acidity and Brix

Below displays brix and acidity tests for wine grapes at WMARS from August 27.

Pests and other considerations

• Grape phomopsis and black rot continues to be observed in West Madison. Black rot fruit infections have been reported across much of Wisconsin. Black rot fruit infections will eventually shrivel into a blue/black hardened fruit “mummy”.
• Growers should keep an eye out for sour rot and botrytis bunch rot, especially around veraison. Check out last week’s article on summer fruit rots.
• Spotted wing drosophila has been observed at West Madison. Continue monitoring traps and using NEWA models.
• Sap beetles have been observed feeding on over ripe and damaged fruit. Review best management practices here.
• Wasps are becoming more active. Review this Wisconsin Fruit News article from 2020 for more information on wasp monitoring and management: September 3, 2020 Scouting Report.
• Overview of grape insect/mite monitoring and management: Grape Insects and Mite Pests, 2024 Field Season (Cornell, 2024).
• Wisconsin grape growers can reference the Midwest Fruit Pest Management Guide (MFPMG) for a list of registered products and recommended best practices. View the MFPMG Online or order a hard copy here: MFPMG Hard Copy.

Apples

Phenology

In southern Wisconsin, Zestar! has been fully picked and fruit in general are beginning to color up significantly. Gala has been building in sugar content in the last two weeks, and will be ready for a first color pick soon.

Growing Degree Day (GDD) Accumulations
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. Growing degree day (GDD) accumulation in 2023, 2024 and 2025 as of August 27 (January 1 start date; base 43°F BE*).

Note: The Sturgeon Bay NEWA weatherstation is out of service and is not included in this report.

Location	2025	2024	2023
Verona WMARS	3251	3313	3326
Gays Mills	3245	3268	3237
Eau Claire	3014	2958	3037
Fond Du Lac	2999	3238	3174
Racine	3133	3421	3102

*BE = Baskerville-Emin calculation method

Other considerations:

• Continue to keep an eye on degree-day accumulation for codling moth  based on trap biofix in your area.
• Apple maggot will emerge through September. Growers should continue using red sphere traps to monitor fall population levels.
• Check out the WI DATCP Orchard Insect Pest Bulletin for more information on current insect trap captures across the state.
• Sooty blotch and flyspeck continues to be observed in Southern WI. Continue monitoring NEWA models and scout susceptible varieties.
• Sun scald and southwest injury to trunks and branches has been observed across many orchards and vineyards this summer, likely due to wide variations in winter temperatures that can cause trunk and branch damage.
• Fruit sunburn and bird injury has been observed across many fruit crops in southern WI. Consider removing this fruit while out picking to prevent other pests attracted to the volatiles released from impacting fruit.
• Bitter pit and cork spot have been observed in southern Wisconsin, driven by high moisture levels. Review best management practices here.

That’s all for this week – good luck to all WI Fruit Growers!

This article was posted in Apples, Disease, Grapes, Insects and tagged Amaya Atucha, Apples, Courtney Meeks, disease, gdd, Grape Acidity, Grape Brix, Grapes, growing degree day accumulations, Growing Degree Days, insects, Josie Dillon, Leslie Holland, pests, phenology, Wisconsin Fruit Crop Scouting Report.