Phenology

We are anxiously awaiting harvest for our last three cultivars at WMARS: Frontenac, Marquette, and Petite Pearl. At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoots from primary buds average around E-L* 38 (Berries harvest ripe). Brianna was harvested on 9/1 and LaCrescent on 9/6. The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of September 18 was 48°F. 

At the Penisular Agricultural Research Station (PARS) in Sturgeon Bay, WI, shoots from primary buds average around E-L* stage 37 (Berries not quite ripe) in Marquette. The minimum air temperature recorded at NEWA weather station at Sturgeon Bay for the early morning of September 18 was 47°F. 

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

Insect Pests and Diseases

With disease pressure remaining low, we are not observing any pathogens at this time. We are monitoring NEWA as well as weekly scouting to keep an eye on our grape clusters. 

With the increase in sugar content of our grapes, wasp presence has increased. They were observed in all cultivars that still have fruit on the vine. 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 September 18 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 September 18, 2023 (April 1 start date; base 50°F BE*) at the WMARS and PARS. 

Location	2023	2022	2021
WMARS	2659	2558	2736
PARS	1980	2002	2098

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of September 18 (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.

	pH
Cultivar	8/17	8/22	8/29	9/6	9/13	9/20
Brianna	3.1	3.14	3.38	Harvested	Harvested	Harvested
Frontenac	2.91	2.92	3.02	3.11	3.15	3.23
LaCrescent	2.97	2.97	3.05	3.13	Harvested	Harvested
Marquette	2.92	2.94	3.01	3.1	3.14	3.2
Petite Pearl	2.92	3.03	3.14	3.29	3.41	3.44
	TA
Cultivar	8/17	8/22	8/29	9/6	9/13	9/20
Brianna	8.93	7.42	6.07	Harvested	Harvested	Harvested
Frontenac	24.78	19.03	18.24	15.45	14.62	14.58
LaCrescent	23.98	19.39	18.35	16.21	Harvested	Harvested
Marquette	22.42	16.86	16.05	13.43	11.84	11.9
Petite Pearl	18.16	12.69	9.55	7.88	7.39	7.16
	Brix
Cultivar	8/17	8/22	8/29	9/6	9/13	9/20
Brianna	15.9	17.3	18.7	Harvested	Harvested	Harvested
Frontenac	17.0	19.6	21	22.8	23.5	25.1
LaCrescent	19.3	21.1	21.1	24.5	Harvested	Harvested
Marquette	18.4	20.8	22	24.2	24.3	25.6
Petite Pearl	12.2	13.9	16.1	18.2	18.5	20.2

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