Phenology

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoots from primary buds average around E-L* 36 (Berries with intermediate sugar levels) in Petite Pearl and 37 (Berries not quite ripe) in Marquette. We are anticipating harvesting Brianna next week. All grapes are officially covered with bird netting. The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of August 21 was 64.6°F. 

At the Penisular Agricultural Research Station (PARS) in Sturgeon Bay, WI, shoots from primary buds average around E-L* stage 35 (Berries begin to color and enlarge) in Marquette. The minimum air temperature recorded at NEWA weather station at Sturgeon Bay for the early morning of August 21 was 58.9°F. 

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

Insect Pests and Diseases

The only foliar diseases observed were in the Petite Pearl grapes. There were some pockets of Black Rot. This variety is known to be susceptible to Black Rot. However, since the grapes are no longer susceptible, we will not be taking fungicide action. We are anticipating one more spray before harvest to protect clusters from bunch rots. 

Phylloxera galling is still seen in the vineyard. Since clusters are beyond bunch closure and the incidence is below 10% of the total canopy we do not plan to apply any insecticide to control phylloxera for the remainder of the season.  To read more about grape phylloxera and management recommendations, click here. 

Japanese Beetle presence and defoliation injury are still primarily in the Petite Pearl grapes and some injury was also observed in the Marquette. Since damage is less than the 30% defoliation threshold, no insecticide will be applied for Japanese beetles this week. For more information about Japanese beetle management, please click here. 

Social wasps are starting to pick up in grapes at WMARS as well as at vineyards where we are conducting research in Southern Wisconsin. Wasps are looking for food and come to grapes and other fruit crops in search of sugar. While some wasps will attack previously damaged or split grapes, others are able to cut the skin of the fruit to access the pulp. If you are considering insecticides for managing wasps, remember that no insecticide has wasps on the label but that you can still apply an insecticide, provided it is registered on the type of crop you plan to spray for wasps. For more information about social wasps, please click here.

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through August 21 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 21, 2023 (April 1 start date; base 50°F BE*) at the WMARS and PARS. 

Location	2023	2022	2021
WMARS	2165	2066	2213
PARS	1756	1651	1774

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of August 21 (Starting April 1) at WMARS and PARS for 2021, 2022, and 2023. 

The graphs and tables below present fruit quality data Brix, TA, and pH from berries sampled from the West Madison Agricultural Research Station (WMARS) in Madison, WI.

	Brix
Cultivar	8/17	8/22
Brianna	15.9	17.3
Frontenac	17.0	19.6
LaCrescent	19.3	21.1
Marquette	18.4	20.8
Petite Pearl	12.2	13.9

	TA
Cultivar	8/17	8/22
Brianna	8.93	7.42
Frontenac	24.78	19.03
LaCrescent	23.98	19.39
Marquette	22.42	16.86
Petite Pearl	18.16	12.69

	pH
Cultivar	8/17	8/22
Brianna	3.1	3.14
Frontenac	2.91	2.92
LaCrescent	2.97	2.97
Marquette	2.92	2.94
Petite Pearl	2.92	3.03

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