Hello fruit growers, we are excited to share apple and grape scouting updates with you this year through the Wisconsin Fruit Newsletter. Much of the state has seen a large amount of rain with hot, humid temperatures in the past two weeks. Several areas in Southern Wisconsin received 3+” of rain which has boosted disease pressure in many fruit crops. 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 29 (berries pepper-corn size, bunches tending downwards) on Petite Pearl and Frontenac to E-L stage 32 (Beginning of bunch closure, berries touching) in Brianna and Marquette. At the Peninsular Agricultural Research Station (PARS) all cultivars are around E-L stage 26-29 (cap fall to peppercorn).

*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 2 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 2, 2025 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

Location	2025	2024	2023
Verona WMARS	1017	1079	1116
Sturgeon Bay PARS	661	695	788

*BE = Baskerville-Emin calculation method

Pests and other considerations

• Grape phomopsis and black rot continues to be observed in West Madison. A reminder that most pesticides will wash off after ~1 inch of rain.
• Early to late-stage phylloxera continues to be observed in West Madison, keep an eye out for galls while scouting. Use a 10x hand lens to inspect trunks and canes for presence/movement from root system to leaves. Once the gall is formed on leaves, it offers a protective layer from any pesticides deployed targeting phylloxera, making it less effective.
• Initial Downy mildew foliar symptoms (“oil spots”) have been observed in West Madison. This week at West Madison, Revus (mandipropamid; FRAC 40) and Endura (boscalid; FRAC 7) were applied for summer diseases.
• Shoot thinning reminder: Thin shoots down to ~2 per spur to improve light penetration, aid in air flow, and keep vines healthy. Reminder: Spurs should be spaced between 4-6 inches, and we are aiming for 2 shoots/spur.
• 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, Ida Red) have reached ~1.5 inches (38-42mm) in diameter while later cultivars (Fuji, Honeycrisp) have reached ~1 inch (~30-34mm) in southern Wisconsin. Varieties at PARS are quite a bit behind compared to West Madison: Zestar is at 26-30mm while Honeycrisp is at 20-24mm. 

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

Location	2025	2024	2023
Verona WMARS	1642	1760	1643
Gays Mills	1664	1726	1661
Eau Claire	1487	1492	1581
Door County PARS	1129	1243	1240
Fond Du Lac	1448	1703	1559
Racine	1454	1770	1447

*BE = Baskerville-Emin calculation method

Other considerations:

• Second generation codling moth will emerge around 1250 DD base 50℉ from the initial biofix. Continue monitoring traps weekly and refresh lures.
• Apple maggot was captured in southern WI. Growers can use red sphere traps to monitor populations and establish a biofix date. Read more information on apple maggot monitoring/management in the linked article.
• Woolly apple aphid has been observed in southern WI, check for white “cottony” appearing tufts where leaf petioles meet branches.
• Check out the WI DATCP Orchard Insect Pest Bulletin for more information on current insect trap captures across the state.
• Warm and rainy weather have also brought early reports of bitter rot in some orchards; see the article on bitter rot management in this week’s newsletter
• Need insect scouting supplies, lures or traps? Place your order here: Great Lakes IPM
• 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.