Phenology

Petite Pearl was harvested last week. This levels on Marquette and Frontenac, which is planned to be harvested Thursday and Friday this week. By the time you read this, we will hopefully be done if not near done with our 2023 harvest. 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, LaCrescent on 9/6, and Petite Pearl on 9/28-29 . The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of October 2 was 60.1°F. 

Marquette was harvested at the Penisular Agricultural Research Station (PARS) on Tuesday, September 3rd. The minimum air temperature recorded at the nearby NEWA weather station at Bailey’s Harbor for the early morning of October 2 was 60.4°F. 

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

Insect Pests and Diseases

Some powdery mildew was observed on the Marquette vines at PARS. This was only seen on the leaves and not fruits. At WMARS, the rain last week (~3 inches in 3 days) brought a lot of gray mold (Botrytis cinerea) to the Petite Pearl vines. Berry wounding due to the high wasp incidence before the rains provided ideal conditions for fungal infections. During grape harvest, wasp presence was moderate to high. The last grapes on the vine, Marquette and Frontenac, look good with no signs of pests or diseases. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through October 2 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. Note that PARS is not included past the last vineyard scouting report due to the weather station being down for maintenance. 

Growing degree day accumulation as of September 18, 2023 (April 1 start date; base 50°F BE*) at the WMARS. 

Location	2023	2022	2021
WMARS	2905	2665	2947

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of October 4 (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	9/28	10/4
Brianna	3.1	3.14	3.38	Harvested	Harvested	Harvested	Harvested	Harvested
Frontenac	2.91	2.92	3.02	3.11	3.15	3.23	3.25	3.28
LaCrescent	2.97	2.97	3.05	3.13	Harvested	Harvested	Harvested	Harvested
Marquette	2.92	2.94	3.01	3.1	3.14	3.2	3.23	3.31
Petite Pearl	2.92	3.03	3.14	3.29	3.41	3.44	3.51	Harvested
	TA
Cultivar	8/17	8/22	8/29	9/6	9/13	9/20	9/28	10/4
Brianna	8.93	7.42	6.07	Harvested	Harvested	Harvested	Harvested	Harvested
Frontenac	24.78	19.03	18.24	15.45	14.62	14.58	13.77	12.76
LaCrescent	23.98	19.39	18.35	16.21	Harvested	Harvested	Harvested	Harvested
Marquette	22.42	16.86	16.05	13.43	11.84	11.9	11.05	9.01
Petite Pearl	18.16	12.69	9.55	7.88	7.39	7.16	6.456	Harvested
	Brix
Cultivar	8/17	8/22	8/29	9/6	9/13	9/20	9/28	10/4
Brianna	15.9	17.3	18.7	Harvested	Harvested	Harvested	Harvested	Harvested
Frontenac	17.0	19.6	21	22.8	23.5	25.1	25.1	27.3
LaCrescent	19.3	21.1	21.1	24.5	Harvested	Harvested	Harvested	Harvested
Marquette	18.4	20.8	22	24.2	24.3	25.6	25.7	27
Petite Pearl	12.2	13.9	16.1	18.2	18.5	20.2	21.7	Harvested

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.