Hello fruit growers, we are excited to share apple and grape scouting updates with you this year through the Wisconsin Fruit Newsletter. It has been quite wet with just over two inches of rain that fell in Southern Wisconsin in the past two weeks.

Several secondary insects have been observed, including green apple aphid, woolly apple aphid, phylloxera, mites and leafhoppers.

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 31-34 (berries begin to soften, sugar starts increasing). At the Peninsular Agricultural Research Station (PARS) all cultivars are around E-L stage 26-27 (setting, young berries enlarging). 

*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. Berries are sizing up and summer rots have been observed at West Madison. Continue scouting and keeping an eye on the NEWA models in your area. Degree day accumulation in 2026 has been similar to the past two seasons.

Growing degree day (GDD) accumulation as of July 2, 2026 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

Pests and Other Considerations

Pre-bloom through bloom is a critical time for disease management to limit fruit infections. During this window, leaves, flowers, and developing fruit are highly susceptible to infection by several important fungal pathogens, including black rot, Phomopsis cane and leaf spot, powdery mildew, downy mildew, and Botrytis gray mold. Check out Dr. Leslie Holland’s article on Protecting Grape Clusters During the Critical Pre-Bloom to Post-Bloom Period.

Make sure newly planted fruit crops are getting enough water in this heat. 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.

Downy mildew foliar symptoms (“oil-stains”) have been observed in West Madison. Scout for pale-yellow lesions on the tops of leaves and white downy growth on the underside of leaves.

Recent rain has driven infection events for black rot and phomopsis. Keep an eye out for developing leaf lesions. Check the linked article for further information on scouting and management.

Phylloxera galls have increased significantly in the past week with the warmer temperatures and rain. Check out the linked article for further information on scouting and management.

Petiole nutrient sampling during bloom: collect the leaves opposite the first or second flower cluster of a shoot. Aim for about 50 percent bloom and try to hit the same stage each year, since nutrient levels can shift over the bloom period. Check out Dr. Amaya Atucha’s article on Petiole Sampling for Determining Fertilization Needs in Cold Climate Grapes.

Apples

Phenology

Early apple cultivars (Zestar, Ida Red) have reached 2.5”+ in diameter while later cultivars (Gala, Honeycrisp, McIntosh) have reached 1.5”+ in southern Wisconsin. Varieties at PARS are quite a bit behind compared to West Madison: most varieties are between ½” and 1”. Remember to record petal fall and biofix dates at several blocks/cultivars in your orchard, to use in the NEWA models this summer. Make sure to check codling moth traps daily when nighttime conditions are calm, warm and humid and watch for an influx of captures that may indicate second generation flight.

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 July 2 is roughly similar to what we observed during the 2024 season. Temperatures in the next week will remain warm, in the upper 80’s and low 90’s, and wet in Southern Wisconsin. Expect fruit development and degree-day accumulation to steadily increase.

Growing degree day (GDD) accumulation in 2024, 2025 and 2026 as of July 2 (January 1 start date; base 43°F BE*).

Pests and Other Considerations