Correction to note: The titratable acidity value for Frontenac from September 1 was corrected from 9.6 to 19.5 g/L tartaric acid equivalence in Table 1 and Figure 2, as well as related sentences, in the last report.

Phenology

At the West Madison Agricultural Research Station (WMARS) in Madison, WI, harvesting continues along the following schedule:

Brianna and Itasca: September 4

La Crescent: September 11

Crimson Pearl and Petite Pearl: September 15

Marquette: September 18

Frontenac: September 28

Fruit Ripening Metrics

From veraison until harvest, we reported the fruit ripening chemistry metrics for the cultivars at WMARS, measures that are typically used to gauge timing of harvest for cold climate grapes: total soluble solids (TSS; sugars, primarily; measured in Brix %), titratable acidity (TA, measured as tartaric acid equivalents in g/L), and pH. We measured sugars using a digital refractometer (Model HI96801, Hanna Instruments) and the TA and pH using an automatic titration system (Model HI902c, Hanna Instruments). Each value reported here is an average from pooled berry samples (about 45 berries in each, taken from both sides of the canopy) collected from panels of four vines located in two different parts of the vineyard. Crimson Pearl and Petite Pearl berry samples were collected from single vines in their respective panels because the other vines are being used for a research study.

Current measurements were taken on September 22 and 28 (Table 1), both for Frontenac (Table 1).

Figures 1, 2, and 3 show the complete data for the total soluble solids, TA, and pH, respectively, for all of the red and white cultivars grown at WMARS this growing season.

Table 1. Fruit ripening chemistry metrics of sugars, titratable acidity (TA), and pH, for Frontenac grown at the West Madison Agricultural Research Station (WMARS). Current berry samples were collected and analyzed on September 22 and 28.

Cultivar: Frontenac*	Brix (%)	TA (g/L)	pH
9/22	21.0	17.0	3.2
9/28	22.3	16.1	3.2

*Harvested 9/28.

Growing Degree Day (GDD) Accumulations

Depicted in Table 2 and on the graph in Figure 4 are the GDD accumulations from April 1 through September 28 for this season and the past two seasons at the WMARS and the Peninsular Agricultural Research Station (PARS). Currently at both locations, the GDD accumulations for the past two weeks have been similar those over the prior two weeks. As a result, the total 2020 heat experience at WMARS is more similar to that of 2019, while the temperature experience at PARS is more similar to that for 2018.

We use the NEWA website as our source for GDD data. You can visit their “About degree days” page to learn more about the concept of degree days and the formulas used in calculations.

Table 2. Growing degree day accumulation as of September 28, 2020 (April 1 biofix date; base 50 °F BE*) at the West Madison Agricultural Research Station (WMARS) and the Peninsular Agricultural Research Station (PARS).

Location	2020	2019	2018
WMARS	2597.1	2554.0	2859.8
PARS	2140.7	1895.1	2260.8

*BE = Baskerville-Emin calculation method

This article was posted in Grapes and tagged Amaya Atucha, Andi Nelson, Beth Ann Workmaster, fruit ripening metrics, grape phenology, Grapes, grapes developmental stages, growing degree day accumulations.