Hello fruit growers, we are excited to share apple and grape scouting updates with you this year through the Wisconsin Fruit Newsletter. Recent rain events have pushed along spore maturity and disease infection events for apple scab and cedar apple rust in apples, and Phomopsis cane and leaf spot and black rot in grapes. Insects are more active as well, with several growers reporting codling moth trap captures and observations of plum curculio and grape phylloxera. 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. This weekend we are expecting intense heat and humidity, with temperatures reaching 95–98°F (35–36°C) across much of the state. Please refer to the Prepare Your Fruit Crops for This Weekend’s Heat and Humidity article.

Grapes

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 21-23 (30%-50% Caps Off) on Petite Pearl to E-L stage 29-31 (Berries Peppercorn to Pea Size) in LaCrescent. At the Peninsular Agricultural Research Station (PARS) all cultivars are around E-L stage 17 (inflorescence well developed. 

*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 June 18 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. We remain slightly behind in West Madison and PARS compared to the last two years. Growers have reported signs of cane death, likely due to cold temperatures in January with no to very little snow cover.

Growing degree day (GDD) accumulation as of June 18, 2025 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

Location	2025	2024	2023
Verona WMARS	654	800	793
Sturgeon Bay PARS	382	498	517

*BE = Baskerville-Emin calculation method

Pests and other considerations

• Grape phomopsis has been observed in West Madison. See photos below. Read more about phomopsis management in last week’s WI Fruit News here.
• Grape black rot has been observed at West Madison. See photos below. Read more about black rot management in this week’s WI Fruit News here.
• Early to late-stage phylloxera has been observed in West Madison, keep an eye out for galls while scouting.
• 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. We recommend you avoid shoot thinning this weekend during the heatwave to minimize potential sunburn.
• European red mites (ERM) and predatory red velvet mites have been observed in West Madison in low to moderate populations. Scout ~50 leaves per block to assess ERM population pressure.
• Overview of grape insect/mite monitoring and management: Grape Insects and Mite Pests, 2024 Field Season (Cornell, 2024)

Apples

Phenology

Early apple cultivars (Zestar, Ida Red) have reached ~1.5 inches (35-40mm) in diameter while later cultivars (Fuji, Honeycrisp) have reached ~1 inch (25-30mm) in southern Wisconsin. Varieties at PARS are quite a bit behind compared to West Madison: Zestar is at 22-26mm while Honeycrisp is at 16-20mm. Remember to record petal fall dates at several blocks/cultivars in your orchard, to use in the NEWA models this summer.

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.  Similar to grapes, degree day accumulation (Base 43°F BE*) between January 1 and June 18 continues to be slightly behind compared to last year in central and Southern Wisconsin. The extreme heat this weekend (90℉+) will give development a boost.

Growing degree day (GDD) accumulation in 2023, 2024 and 2025 as of June 18 (January 1 start date; base 43°F BE*).

Location	2025	2024	2023
Verona WMARS	1181	1383	1221
Gays Mills	1212	1376	1241
Eau Claire	1063	1180	1166
Door County PARS	752	949	872
Fond Du Lac	1011	1348	1139
Racine	979	1386	1057

*BE = Baskerville-Emin calculation method

Pests and other considerations:

• Continue scouting for and pruning out shoot blight. Check for the classic “shepherds crook” symptom and prune back 12-18” from the point of infection. See the recent shoot blight management reminders in this week’s newsletter.
• Cedar apple rust has been observed in West Madison. Scout for yellow/orange lesions on leaves and developing fruit (see photo below). 
• Growers are beginning to apply codling moth insecticides as we reach 250 DD base 50℉ from the biofix. As a reminder, a biofix occurs when an influx of ~5+ moths are cumulatively captured across traps, or captured on consecutive days (sustained capture). Second generation codling moth will emerge around 1250 DD base 50℉.
• Plum curculio oviposition injury continues to be observed in southern Wisconsin (see photo below). Growers should continue scouting for signs of movement further into the orchard. West Madison had a petal fall date of 5/16 and hit 308 degree days base 50℉ on June 13. Once 308 degree-days base ℉ have accumulated from the petal fall date, typically PC cease movement into the orchard and no longer require control.
• 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

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.