Hello grape growers, I’m excited to share grape scouting updates with you again this year through the Wisconsin Fruit Newsletter. I’m Courtney C Meeks, a graduate student in the Holland Fruit Crop Pathology lab researching diseases of cold-climate wine grapes. 

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 3 (Wooly bud 土 green showing) on Petite Pearl and Brianna to 4 (Budburst; leaf tips visible) in Marquette and LaCrescent. At the Peninsular Agricultural Research Station (PARS) all cultivars are at bud swell stage.

There were some frost events last week in areas around Wisconsin. You read more about scouting for frost damage here. The days are becoming warmer, but night time temperatures are staying cool. We are anticipating budburst in the next week or so and are watching our buds. We are still keeping an eye on the weather for any possibility of a late frost. You might notice in the photos that our spurs are still a little long (~5-6 buds per shoot). This was done back in March to prevent any buds from swelling during the handful of warm days. You can read more about this here, but we will prune back to a two count bud after Mother’s Day. 

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of April 30 was 43°F. 

*E-L stands for Eichhorn-Lorenz growth stages scale to describe grapevine development. 

Pests

There were not any signs of diseases or insect pests at WMARS. As the temperatures continue to warm, we will be on the lookout. Dandelions and other weeds are starting to emerge, and we anticipate an herbicide application at the research station vineyards before the rain later this week. Special attention should be paid to flea beetle and cutworms that may be feeding on developing buds. Once buds burst open, there is no need to treat for flea beetle and cutworms.

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through April 30 for the past three seasons. Our current season appears to be on track with 2023. You can see the increase in GDD earlier in the month, which corresponds to those warm days we had earlier this month. 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 accumulation as of April 30, 2024 (April 1 start date; base 50°F BE*) at the WMARS. 

Location	2024	2023	2022
WMARS	99	105	38

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of April 30 (Starting April 1) at WMARS for 2022, 2023, and 2024.

Cheers to another year!

This article was posted in Grapes and tagged Amaya Atucha, Christelle Guédot, Courtney C Meeks, grape phenology, growing degree day accumulations, Leslie Holland, phenology, vineyard scouting.