Phenology

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 5 was 71.3°F. 

At the Peninsular 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 5 was 63.9°F. 

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

Insect Pests and Diseases

Disease pressure has remained low with only black rot observed on the Petite Pearl; this variety is highly susceptible. Most infections are localized to the lower parts of the canopy’s foliar tissue. At this point in the season, we will not be applying any fungicides as the fruit is no longer susceptible to infections. We are monitoring NEWA to see if any environmental conditions become conducive. 

We continue to see social wasps but in low numbers at WMARS. Other vineyards around Wisconsin are seeing higher wasp pressure as the season progresses. Wasp nests are likely pretty well loaded with wasps at this time and lots of wasps are out looking for sugar. 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 5 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 5, 2023 (April 1 start date; base 50°F BE*) at the WMARS and PARS. 

Location	2023	2022	2021
WMARS	2501	2354	2527
PARS	2009	1918	2045

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of September 5 (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
Brianna	3.1	3.14	3.38	Harvested
Frontenac	2.91	2.92	3.02	3.11
LaCrescent	2.97	2.97	3.05	3.13
Marquette	2.92	2.94	3.01	3.1
Petite Pearl	2.92	3.03	3.14	3.29
	TA
Cultivar	8/17	8/22	8/29	9/6
Brianna	8.93	7.42	6.07	Harvested
Frontenac	24.78	19.03	18.24	15.45
LaCrescent	23.98	19.39	18.35	16.21
Marquette	22.42	16.86	16.05	13.43
Petite Pearl	18.16	12.69	9.55	7.88
	Brix
Cultivar	8/17	8/22	8/29	9/6
Brianna	15.9	17.3	18.7	Harvested
Frontenac	17.0	19.6	21	22.8
LaCrescent	19.3	21.1	21.1	24.5
Marquette	18.4	20.8	22	24.2
Petite Pearl	12.2	13.9	16.1	18.2

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.