Hello fruit growers, we are excited to share apple and grape scouting updates with you this year through the Wisconsin Fruit Newsletter. Rain continues to be persistent, with occasional thunderstorms bringing high humidity and warm temperatures. These conditions have been ideal for summer diseases in apples and grapes. 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. 

Grapes

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 32 (Beginning bunch closure, berries touching) on Petite Pearl, Frontenac and La Crescent to E-L stage 34 (Berries begin to soften) in Brianna and Marquette. At the Peninsular Agricultural Research Station (PARS) all cultivars are around E-L stage 31 (Berries pea-sized). 

*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 July 16 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 July 16 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

Location	2025	2024	2023
Verona WMARS	1350	1401	1411
Sturgeon Bay PARS	935	985	1048

*BE = Baskerville-Emin calculation method

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”.
• Japanese beetles have been observed at West Madison and will continue to emerge through September. Females prefer to lay eggs in areas with short grass and high soil moisture, about 2-4” into the soil. Consider pausing mowing and watering through mid-August to deter egg laying.
• Overview of grape insect/mite monitoring and management: Grape Insects and Mite Pests, 2024 Field Season (Cornell, 2024).
• 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.
• Don’t forget to collect petiole samples for nutrient analysis at veraison—this is the standard timing to assess vine nutrient status and guide fertilization decisions.

Apples

Phenology

Early apple cultivars (Zestar) have reached 45-50mm in diameter while later cultivars (Honeycrisp) have reached 40-45mm in southern Wisconsin. Varieties at PARS are quite a bit behind compared to West Madison: Zestar is at 35-40mm while Honeycrisp is at 30-35mm. 

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 July 16 (January 1 start date; base 43°F BE*).

Location	2025	2024	2023
Verona WMARS	2073	2180	2036
Gays Mills	2092	2137	2027
Eau Claire	1902	1884	1919
Door County PARS	1501	1631	1598
Fond Du Lac	1858	2120	1966
Racine	1893	2207	1854

*BE = Baskerville-Emin calculation method

Other considerations:

• Second generation codling moth initial flights have been observed in Southern WI. Typically, second generation moths will emerge around 1250 DD base 50℉ from the initial biofix. Continue monitoring traps weekly and refresh lures.
• Apple maggot will continue to emerge through September. Growers can use red sphere traps to monitor populations and establish a biofix date. 
• Woolly apple aphid has been observed in southern WI, check for white “cottony” appearing tufts where leaf petioles meet branches.
• Japanese beetles have been observed at West Madison and will continue to emerge through September.
• Check out the WI DATCP Orchard Insect Pest Bulletin for more information on current insect trap captures across the state.
• Need insect scouting supplies, lures or traps? Place your order here: Great Lakes IPM
• Warm and rainy weather have also brought early reports of bitter rot in some orchards; see the article on bitter rot management from the July 4 newsletter.
• Sooty blotch and flyspeck has been observed in Southern WI, pushed along by warm, humid conditions. Continue monitoring NEWA models.
• In this heat, make sure newly planted apple trees are getting enough water. Without irrigation, growth can stall during establishment. Irrigation frequency depends on soil type—sandy soils need water daily or every two days, while heavier soils like silt or clay can be watered less often by applying several days’ worth of water at once.
• Growers managing return bloom on Honeycrisp should consider starting the Ethrel program. Be cautious with high temperatures—avoid spraying if forecasts show temps near or above 85°F.

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, Grapes, growing degree day accumulations, Growing Degree Days, insects, Josie Dillon, Leslie Holland, pests, phenology, Wisconsin Fruit Crop Scouting Report.