Hello grape growers, it’s officially May, and with it, the anticipation of the season is in full swing!

Phenology

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 12 (5 leaves separated; shoot 10 cm long; inflorescences clear). At the Peninsular Agricultural Research Station (PARS) the Itasca vines are at budburst with the Marquette are at budswell to wooly stade.

There is a lack of uniformity in our bud development, probably due to the long pruning we implemented to delay bud break of buds located at the base of spurs. This week we completed our final pruning in which we only left 2 count buds per spur (Figure 1). In general, the base buds were significantly delayed in development, but we anticipate they will catch up with more developed buds.

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

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of May 13th was 59°F.

Pests

There were some Phomopsis and black rot lesions on LaCrescent vines. However, the black rot lesions lacked the spore-bearing structures of the fungus, meaning these lesions are not active. Since last week, there have been two to three days where conditions were suitable for infections. To view conditions and predicted disease events in your area, consult the Grape Disease Models on NEWA.  Rain and high winds have made applying pesticides challenging over the last couple of weeks, and our first fungicide application of the season will be applied on May 15 to wine and table grape varieties. Special attention should be paid to flea beetles and cutworms that may be feeding on developing buds. Once buds burst open, there is no need to treat flea beetles and cutworms.

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through May 13 for the past three seasons. Our current season appears to be on track with 2023. 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 13, 2024 (April 1 start date; base 50°F BE*) at the WMARS.

Location	2024	2023	2022
WMARS	248	260	207
PARS	122	158	N/A**

*BE = Baskerville-Emin calculation method

** The weather station at PARS was not operational in 2022

Accumulation of growing degree days (GDD) as of May 13 (Starting April 1) at WMARS for 2022, 2023, and 2024.

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