Phenology

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoots from primary buds average around E-L* stage 33 (Berries still hard and green) in Petite Pearl and 35 (Berries begin to color and enlarge) in Marquette and Brianna. The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of July 24 was 63.4°F. 

At the Penisular Agricultural Research Station (PARS) in Sturgeon Bay, WI, shoots from primary buds average around E-L* stage 32 (Beginning of bunch closure, berries touching) in Marquette. The minimum air temperature recorded at NEW weather station at Sturgeon Bay for the early morning of July 24 was 61.2°F. 

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

Insect Pests and Diseases

Disease symptoms were not observed. The high heat and dry conditions are not conducive to most pathogens. However, we are keeping an eye out on the potential for powdery mildew. Other southern vineyards have observed powdery mildews; you can read more about this in a recent article. In the Petite Pearl grapes, we did notice shriveling and purpling of some berries (Picture 1) and groups of berries in the cluster. This is not black rot, which starts as brown discoloration and will produce fruiting bodies, nor late stem bunch necrosis in which the rachis and pedicel of the cluster dehydrates and breaks down resulting in shriveled berries.  Instead, this is probably the result of heat and water stress experienced this season. We will continue monitoring how the clusters with dehydrated berries develop during the rest of the season. 

Phylloxera galling was centered on young leaves in the outer parts of the canopy. Every variety had severe galling specifically in these clustered sections of the canopy. To read more about phylloxera and management recommendations, click here. We are seeing Japanese beetle damage in the vineyard, specifically in the Petite Pearl grapes. While the damage, characterized by the skeletonization of the leaves, can be observed on a few leaves, the occurrence of seeing an actual beetle was low (only 4).  For more information about Japanese beetle management, please click here.

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through July 24 for the past three seasons. This data is collected using the NEWA degree day calculator. 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 24, 2023 (April 1 start date; base 50°F BE*) at the WMARS and PARS. 

Location	2023	2022	2021
WMARS	1562	1516	1592
PARS	1229	1145	1203

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of July 24 (Starting April 1) at WMARS and PARS for 2021, 2022, and 2023. 

This article was posted in Grapes and tagged Amaya Atucha, Christelle Guédot, Courtney Cameron, grape phenology, Grapes, Leslie Holland, vineyard scouting.