Phenology

This week at the West Madison Agricultural Research Station (WMARS) in Verona, WI, cultivars are at various stages of setting and developing berries, ranging from E-L* Stage 29 (Berries pepper-corn size (4 mm diam.); bunches tending downwards) to Stage 32 (Beginning of bunch closure, berries touching (if bunches are tight)). The setting of fruit on Marquette clusters was more variable due to uneven pollination. Brianna clusters are typically tight and they are now reaching bunch closure.

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

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Figure 1. E-L growth stages of grape cultivars at the West Madison Agricultural Research Station.

Growing Degree-Day (GDD) Accumulations

Depicted in Figure 2 and listed in Table 1 are the GDD accumulations from April 1 to June 20 for this year and the past two seasons. Degree-days were calculated using a base 50 °F, starting on April 1 as a biofix date. We use the NEWA website and the “BE” (Baskerville-Emin) calculation. This method uses a sine wave instead of a simple average temperature calculation, which is thought to provide a more accurate estimation of degree-days. You can visit the NEWA “About degree days” page to learn more about the concept of degree days and the formulas used in calculations. (http://newa.cornell.edu/index.php?page=about-degree-days).

At both WMARS and PARS, the current 2021 season GDD accumulation is continuing to be much greater than for either 2020 or 2019. The current GDD accumulation as of June 20 at WMARS was more than about 200 to 300 units higher than in either of the previous two years. At PARS, the accumulation is about double than it was at this time in 2019 and half again as much as in 2020. The total temperature experience at PARS is currently similar to what was happening at WMARS in 2019 at this point in the season.

Table 1. Growing degree day accumulation as of June 20, 2021 (April 1 biofix date; base 50 °F BE*) at the West Madison Agricultural Research Station (WMARS) and the Peninsular Agricultural Research Station (PARS).

Location	2021	2020	2019
WMARS	903	713	613
PARS	588	400	293

*BE = Baskerville-Emin calculation method

This article was posted in Grapes and tagged Amaya Atucha, Andi Nelson, Beth Ann Workmaster, grape phenology, Grapes, grapes developmental stages.