Being a Georgia native, I thought I left this heat & humidity behind! This duo is a double whammy for grapes. The heat speeds up grape development; while the humidity ensures a majority of the pathogens have an ideal environment for their germination and growth. So I guess me and the pathogens both feel right at home with the heat & humidity?

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, buds average around E-L* stage 31 (Berries pea-size) for Brianna and E-L* stage 27 (Setting; young berries enlarging) for Petite Pearl. 

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of June 17th was 69.8°F. 

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

Pests

Phomopsis cane and leaf spot has been observed on all varieties. Variability in phenology has been observed, especially in the Petite Pearl vines, this season. This variability has been noted at one commercial vineyard as well in Southeastern Wisconsin. This presents challenges for disease management, but the key to success is continuing to switch up the FRAC group applied and monitoring the Grape Disease Models on NEWA. An oil spot was observed on a Marquette vine. With the high humidity currently descending on Wisconsin, scouting for Downy Mildew oil spots in lower areas of your vineyard or on susceptible varieties is important. Anthracnose has been observed in other Southeastern vineyards. In previous years, I haven’t seen anthracnose, but the large amount of rain this season has made it ideal for the pathogen. Typically, symptomatic leaves were closest to the cordon or packed deep in the canopy. Unlike Phomopsis, the inner necrotic spot is larger and darker, and the disease can cause loss of leaf tissue and have a bird-shot appearance. 

Starting last week, black rot fruit and stem infections were observed primarily in the Brianna grapes. These infections are the result of missing a spray. Typically, black rot infections are not seen until later in the season before veraison, but these are earlier than my previous years of observations. In the photo, you will note the stem infections in the background. 

Phylloxera have begun to rear their ugly galling on Frontenac, Brianna, and Petite Pearl. If you want to brush up on your Phylloxera knowledge or need a reminder, give this article a read. The insect damage previously noted on primarily Brianna and some LaCrescent vines (see last article) did not progress from the noted damage. All vines have recovered amazingly well with no sign of damage anymore. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through June 17 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 June 17, 2024 (April 1 start date; base 50°F BE*) at the WMARS. 

Location	2024	2023	2022
WMARS	770	771	700
PARS	479	503	423

*BE = Baskerville-Emin calculation method

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