As we are beginning the end of the season, anticipation is in the air. Harvest has begun around Wisconsin for earlier varieties with some nearing their start in the northern part(s) of the state. All of your hard work since spring is nearing completion. 

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, vines average around E-L* stage 36 (Berries with intermediate sugar levels) for Petite Pearl and stage 37 (Berries not quite ripe) for Marquette. Yesterday, September 10th, our Brianna and LaCrescent vines were harvested. Fruit chemistry for those cultivars can be found at the end of this report to reference and compare to your own numbers. 

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of September 11th was 60.8°F. 

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

Pests

Active downy mildew infections are still present on LaCrescent and Brianna vines with some seen on Petite Pearl. These infections were typically observed in the mid to lower canopy and not in the fruit zone. The berries are no longer susceptible to infection, so, for harvest, it is not a concern. However, we are monitoring the levels of foliar infection as we do not want defoliation of leaves. 

Berry shrivel was observed in Petite Pearl, Marquette, and Frontenac. This phenomenon was coupled with necrosis of the peduncle and pedicel. 

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This has been observed in other vineyards as mentioned in the last scouting report. This is the result of downy mildew infections. You can read a recent article here to learn more. 

Flies were observed in the Petite Pearl grapes. We will not be applying an insecticide for this, but we will be monitoring for rot development since wounds on berries can result in potential infections that could lead to sour rot. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through September 11 for the past three seasons. This data is collected using the NEWA website. 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 11, 2024 (April 1 start date; base 50°F BE*) at the WMARS.

Location	2024	2023	2022
WMARS	2438	2545	2416
PARS	1885	1960	1915

*BE = Baskerville-Emin calculation method

Accumulation of growing degree days (GDD) as of September 11 (Starting April 1) at WMARS and PARS for 2022, 2023, and 2024.

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

Titratable Acidity (g/L)
	Cultivar	7/31/24	8/8/24	8/14/24	8/21/24	8/28/24	9/4/24	9/10/04
Table	MN.1325	33.6	27.8	24.0	20.9	18.7*
Table	MN.1369	25.6	20.5	17.1	14.6*
Table	Mars	22.4	15.9	12.1	9.9*
Table	Reliance	19.9	12.1	9.7*
Table	Somerset Seedless	18.2	14.8	13.3*
Wine	Brianna	21.2	NA	13.8	9.9	8.1	7.9	6.4*
Wine	Frontenac	27.8	NA	23.7	20.0	18.2	18.7	17.6
Wine	La Crescent	27.0	NA	23.4	19.1	21.3	17.6	18*
Wine	Marquette	23.0	NA	20.1	16.3	14.9	15.2	12.9
Wine	Petite Pearl	19.8	NA	18.8	12.2	9.4	10.2	10.3

*Harvested

Brix (°)
	Cultivar	7/31/24	8/8/24	8/14/24	8/21/24	8/28/24	9/4/24	9/10/04
Table	MN.1325	13.6	17.6	19.1	20.6	20.6*
Table	MN.1369	12.4	16.4	17.8	17.5
Table	Mars	7.1	11.7	12.7	14.0
Table	Reliance	11.2	14.7	16.3*
Table	Somerset Seedless	14.1	16.3	16.4*
Wine	Brianna	7.2	NA	15.9	15.9	17.9	21.2	22.7*
Wine	Frontenac	9.3	NA	18.6	18.9	18.4	23.3	25.2
Wine	La Crescent	8.7	NA	18.7	18.5	18.4	22.5	23.5*
Wine	Marquette	13.0	NA	18.5	17.9	19.7	21.0	24.5
Wine	Petite Pearl	8.3	NA	13.0	16.5	13.5	19.9	21.0

*Harvested

This article was posted in Grapes and tagged Amaya Atucha, Courtney C Meeks, gdd, grape phenology, Grapes, growing degree day accumulations, Growing Degree Days, Leslie Holland, Mike North, PARS, phenology, vineyard, vineyard scouting.