Phenology

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 2 (bud scale opening) on Petite Pearl and Brianna to 3 (wooly bud ± green showing) in Marquette. Freeze damage is still evident with buds appearing discolored. With temperatures warming up this week, we anticipate budburst next week in our early season varieties. 

With winter injury being a problem across many vineyards in Southern Wisconsin, be on the lookout after budburst to see which buds have ‘pushed’ from either the primary, secondary, or tertiary buds. Primary buds are more fruitful. If you notice freeze damage, it is very possible that these buds have been lost. However, in cold-climate grapes, secondary buds still produce fruit, but typically, it is less than the primary bud. If both buds are damaged, the tertiary bud will prevail and result in no fruit. 

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of May 2 was 38°F. 

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

Pests

There were not any signs of pests at WMARS. As the temperatures rise this week, we will be on the lookout for any potential pests to report. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through May 2 for the past three seasons. Our current season appears to be greater than last year and closer to the 2021 season. 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 May 1, 2023 (April 1 start date; base 50°F BE*) at the WMARS. 

Location	2023	2022	2021
WMARS	126	53	163

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of May 2 (Starting April 1) at WMARS for 2021,2022, and 2023. 

This article was posted in Grapes and tagged Courtney Cameron, gdd, grape phenology, Grapes, grapes developmental stages, growing degree day accumulations, vineyard scouting.