The start of August was unprecedented—cool mornings and highs in the mid-70’s! It has felt like autumn, and I am not upset. Showers appear to have decreased in frequency, which is allowing fruit to develop beautifully. This and more is covered in this week’s addition of vineyard scouting. 

Phenology 

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, vines average around E-L* stage 35 (Berries begin to color and enlarge) in Petite Pearl and E-L* stage 36 (Berries with intermediate sugar levels) for Brianna. This morning two table grape cultivars, Somerset Seedless & Reliance, were harvested with an anticipated harvest of the remaining cultivar and varieties next week. The cultivars: Marquette, LaCrescent, Frontenac, and Brianna have been netted for over a week now with Petite Pearl netting occurring in the next week or so.  

A lot of vineyards are in the process of green harvesting right now to even out their clusters. We are not doing that at West Madison due to labor and time. The only variety that is the most variable is Petite Pearl with some clusters through veraison and others either still green or with some berries within the cluster that have already turned.

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of August 14th was 60.8°F. 

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

Pests

A fungicide application was applied last Tuesday, August 6th to protect our clusters from any sour or bunch rots. Phomopsis lesions were noticed in Brianna and Marquette, but this fungus is not of concern for vine health and harvest at this stage of the season. Clusters are clean from disease. Any downy mildew that was seen was dried and no longer active. We are not anticipating any additional fungicide applications for the rest of the season, but weekly scouting and weather will guide our decision making. 

On the insect side, insects were sparse. A cicada was stuck in one of the nets, but there was no damage observed. Phylloxera galls are still present, but the level of infestation is low. 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through August 14 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 August 14, 2024 (April 1 start date; base 50°F BE*) at the WMARS.

Location	2024	2023	2022
WMARS	1944	1991	1907
PARS	1429	1544	N/A**

*BE = Baskerville-Emin calculation method

** 2022 data is no longer showing on NEWA’s website for PARS

Accumulation of growing degree days (GDD) as of August 14 (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
Table	MN.1325	33.6	27.8	24.0
Table	MN.1369	25.6	20.5	17.1
Table	Mars	22.4	15.9	12.1
Table	Reliance	19.9	12.1	9.7
Table	Somerset Seedless	18.2	14.8	13.3
Wine	Brianna	21.2	NA	13.8
Wine	Frontenac	27.8	NA	23.7
Wine	La Crescent	27.0	NA	23.4
Wine	Marquette	23.0	NA	20.1
Wine	Petite Pearl	19.8	NA	18.8

Brix (°)
	Cultivar	7/31/24	8/8/24	8/14/24
Table	MN.1325	13.6	17.6	19.1
Table	MN.1369	12.4	16.4	17.8
Table	Mars	7.1	11.7	12.7
Table	Reliance	11.2	14.7	16.3
Table	Somerset Seedless	14.1	16.3	16.4
Wine	Brianna	7.2	NA	15.9
Wine	Frontenac	9.3	NA	18.6
Wine	La Crescent	8.7	NA	18.7
Wine	Marquette	13.0	NA	18.5
Wine	Petite Pearl	8.3	NA	13.0

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.