Walking out my door this morning, it didn’t feel like I was opening my oven – finally. The heat wave over the last several days was no joke. Without those cooler night time temperatures, vines were constantly “on” with little ability to store sugars. In addition, some areas were fearful of vine stress. This and more is discussed in this week’s report. 

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 Brianna. This morning, the last of WMARS’s table grapes were harvested. Now, our primary focus is the wine grapes. 

Recently, there have been rather random downpours. While a sprinkle is greatly appreciated this time of year, intense rain events are not ideal. There have been reports of berry bursts in early season whites such as Itasca and Brianna. 

High sugar content + open wound = rot

Fermenting grapes is a lovely smell – except when it is in your vineyard. As you are walking or driving around your vineyard, be sure to take some deep breaths for stress and rot management. Removal of rotten clusters will reduce the spread and decrease insect visitations.

The minimum air temperature recorded at NEWA weather station at WMARS for the early morning of August 28th was 68.2°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. The berries are no longer susceptible to infection, so, for harvest, it is not a concern. However, we are monitoring the levels of infection as we do not want defoliation of leaves. 

A recent diagnostic case revealed a unique downy mildew infection. If you missed the article, be sure to read it here! 

Interestly, there isn’t much to report on the insect side! 

Growing Degree Day (GDD) Accumulations

Below displays the GDD accumulations from April 1 through August 28 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 28, 2024 (April 1 start date; base 50°F BE*) at the WMARS.

Location	2024	2023	2022
WMARS	2237	2294	2173
PARS	1684	1765	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 28 (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
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
Wine	Frontenac	27.8	NA	23.7	20.0	18.2
Wine	La Crescent	27.0	NA	23.4	19.1	21.3
Wine	Marquette	23.0	NA	20.1	16.3	14.9
Wine	Petite Pearl	19.8	NA	18.8	12.2	9.4

*Harvested

Brix (°)
	Cultivar	7/31/24	8/8/24	8/14/24	8/21/24	8/28/24
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
Wine	Frontenac	9.3	NA	18.6	18.9	18.4
Wine	La Crescent	8.7	NA	18.7	18.5	18.4
Wine	Marquette	13.0	NA	18.5	17.9	19.7
Wine	Petite Pearl	8.3	NA	13.0	16.5	13.5

*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.