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 hot and dry the last two weeks across much of Wisconsin. Apple maggot along with second generation codling moth have been active in apples. Several secondary insects have been observed, including aphids, mites and leafhoppers. Some summer fruit rots have also been observed, including bunch rot in grapes and sooty blotch and flyspeck in apples.

As a reminder, this newsletter will cover apple and grape phenology, general scouting observations, and includes an overview of degree day accumulation in fruit growing regions. Growers can reference the Midwest Fruit Pest Management guide for further information on pest management best practices.

Grapes

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).

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. Berries are sizing up and summer rots have been observed at West Madison. Japanese beetles are continuing to emerge and skeletonize grape leaves. 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 16, 2026 (April 1 start date; base 50°F BE*) at the WMARS and PARS.

• 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”.
• Keep an eye out for summer fruit rots. Check out this video for more information on identification and management recommendations here: Distinguishing and Managing Grape Bunch Rots (UW-Madison Extension).
• 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

It was wonderful to connect with growers at the 2026 Wisconsin Apple Growers Association field day on Tuesday, July 14. Thank you to all who presented and attended the event! Apples are continuing to build size and are starting to color up, likely driven by the heat and humidity. Many growers in southern WI are beginning to pick early varieties, like Lodi. Continue monitoring the NEWA models this summer for summer fruit rots. 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. Continue monitoring apple maggot traps to establish a biofix. Reminder: five captures in a single, unbaited trap or across nearby traps is the threshold for economic damage.

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 16 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 continue to be dry. Expect fruit development and degree-day accumulation to steadily increase. Keep an eye out for summer disease development as well as sun scald in this heat.

Growing degree day (GDD) accumulation in 2024, 2025 and 2026 as of July 16 (January 1 start date; base 43°F BE*).