Just like that, it’s almost August! Veraison has set in for Southern Wisconsin vineyards, so the anticipation for harvest is upon us. We cover that and more in this week’s scouting report!

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, vines average around E-L* stage 34 (Berries begin to soften; sugar starts increasing) in LaCrescent and E-L* stage 35 (Berries begin to color and enlarge) for Marquette. The seedless table grapes cultivar trial at WMARS showed the first signs of veraison about two weeks ago, and we immediately placed the bird nets to protect them from the birds. We anticipate nets being placed on the Horticulture vineyard (Brianna, Frontenac, LaCrescent, and Marquette vines) some time this week. 

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of July 29th was 68.4°F. Earlier in the morning, the vineyard received a good amount of rain in the morning, around 0.12 inches. During my scouting, there was a sprinkle of rain, but most showers remained North of the station. 

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

Pests

A fungicide application was applied last Tuesday, July 21 to target downy mildew. An insecticide was applied to the border vines to control Japanese beetles. The insecticide was not applied to table grapes due to pre-harvest intervals (PHI). The decision to apply an insecticide was made due to the large number of beetles I was observing. As we approach August and the harvest season, insecticide options decrease due to PHI, and a lack of action at this time could mean increased beetle feeding damage that could potentially harm the vines’ ability to overwinter. In true 2024 fashion, there was an unpredicted shower in the evening following the pesticide application. However, based on my scouting, we still secured good coverage.

Scouting this week, I did observe sporulating downy mildew on Brianna leaves. However, the downy mildew was on the lower leaves of the canopy near the vineyard floor. Dead foliar downy mildew infections outnumbered the active infections. Current research suggests that berries are no longer susceptible to infection by powdery mildew or downy mildew. However, if berries are damaged, sour rot and Botrytis bunch rot could become a concern. We may apply one more fungicide prior to harvest, especially if rain events continue; scouting and NEWA will guide that decision. 

On the insect side, the number of Japanese Beetles observed had greatly decreased from the previous week with damage not appearing to have worsened. Phylloxera galling was still seen in the vines, but nothing to warrant worrying. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through July 29 for the past three 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. 

Growing degree day accumulation as of July 29, 2024 (April 1 start date; base 50°F BE*) at the WMARS. 

Location	2024	2023	2022
WMARS	1622	1657	1577
PARS	1128	1251	1150

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of July 29 (Starting April 1) at WMARS and PARS for 2022, 2023, and 2024.

This article was posted in Grapes and tagged Amaya Atucha, Courtney C Meeks, Dead foliar downy mildew, Downy mildew, gdd, grape phenology, Grapes, grapevine downy mildew, growing degree day accumulations, Growing Degree Days, Japanese beetle, Japanese Beetles, Leslie Holland, PARS, phenology, vineyard, vineyard scouting.