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 fire blight in apples, and Phomopsis cane and leaf spot 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.

Grapes

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 13-14 (6-7 leaves separated) on Petite Pearl to E-L stage 16-17 (10-12 leaves separated) in LaCrescent. At the Peninsular Agricultural Research Station (PARS) all cultivars are around E-L stage 12-13 (5-6 leaves separated). 

*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 4 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 4, 2025 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

Location	2025	2024	2023
Verona WMARS	414	541	589
Sturgeon Bay PARS	221	316	385

*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 this week’s WI Fruit News here.
• Early signs of phylloxera have 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.

Apples

Phenology

Early apple cultivars (Zestar, Ida Red) have reached ~1 inch (22-25mm) in diameter while later cultivars (Fuji, Honeycrisp) have reached ~½ inch (12-16mm) in southern Wisconsin. Varieties at PARS are quite a bit behind compared to West Madison: Zestar is at ~½ inch (12-16mm) while Honeycrisp is at 6-10mm. Remember to record petal fall dates at several blocks/cultivars in your orchard, to use in the NEWA models this summer. Plum curculio is out in full force, and growers are beginning to set codling moth biofix. Make sure to check codling moth traps daily when nighttime conditions are calm, warm and humid. 

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 4 is slightly behind compared to last year in central and Southern Wisconsin. While degree day accumulation in Northern Wisconsin and near the Great Lakes are even further behind. This may translate to a wider variance in phenology and pest development across the state. Once temperatures are sustained around the mid 70’s and 80’s, expect fruit development and degree-day accumulation to increase quickly.

Growing degree day (GDD) accumulation in 2023, 2024 and 2025 as of June 4 (January 1 start date; base 43°F BE*).

Location	2025	2024	2023
Verona WMARS	844	1026	921
Gays Mills	872	1021	931
Eau Claire	797	912	895
Door County PARS	493	672	646
Fond Du Lac	701	1001	863
Racine	663	1004	799

*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 should continue monitoring codling moth pheromone traps to establish a clear biofix date. As a reminder, a biofix occurs when an influx of ~5+ moths are cumulatively captured across traps, or captured on consecutive days (sustained capture).
  • Note: Several factors determine the threshold for codling moth biofix, including size and elevation within the orchard, type of pheromone lure used, and if mating disruption is used.
• Plum curculio oviposition injury has been observed in southern Wisconsin (see photo below). Growers should continue scouting for signs of movement further into the orchard. Once 308 degree-days 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 as we move through thinning.

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.