At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoots from primary buds average around E-L* 35 (Berries begin to color and enlarge) in Marquette and Petite Pearl and 36 (Berries with intermediate sugar levels) in Brianna. Bird netting has been on the Marquette, LaCrescent, Brianna, and Frontenac grapes since last week. The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of August 7 was 62.4°F.
At the Penisular Agricultural Research Station (PARS) in Sturgeon Bay, WI, shoots from primary buds average around E-L* stage 33 (Berries still hard and green) in Marquette. The minimum air temperature recorded at NEW weather station at Sturgeon Bay for the early morning of August 7 was 61.2°F.
*E-L stands for Eichhorn-Lorenz growth stages scale to describe grapevine development.
Insect Pests and Diseases
The rain and humidity over the last couple of weeks have been conducive to disease development. Black rot foliar lesions were observed on Petite Pearl, a variety highly susceptible to black rot due to the tight clusters. These infections were found throughout the canopy with approximately 5% infection rate. The critical period for controlling black rot has passed and with low levels of infection, we will not be taking fungicide action.
Phylloxera galling is still pocketed in the upper and outer portions of the canopy. Infections were higher in Brianna and LaCrescent. Since the grapes are past bunch closure, we are unable to apply any insecticide. The worst panels have about 10 – 15% phylloxera galling. To read more about phylloxera and management recommendations, click here.
Japanese beetles were predominantly seen in the Petite Pearl vineyard. Over 20 beetles per row were observed with skeletonized leaves present in some of the worst infested vines. However, we have not yet reached 30% defoliation on those vines and as of now do not plan to spray any insecticide to manage Japanese beetles. For more information about Japanese beetle management, please click here. As we are just around the corner for veraison in the Petite Pearl, we will be applying netting over the plants to prevent bird damage in the next week or so.
Growing Degree Day (GDD) Accumulations
Below displays the GDD accumulations from April 1 through August 7 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 August 7, 2023 (April 1 start date; base 50°F BE*) at the WMARS and PARS.
*BE = Baskerville-Emin calculation method
Accumulation of growing degree days (GDD) as of August 7 (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.