At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoot development across most cultivars (Brianna, Frontenac, Itasca, La Crescent, and Marquette) ranged between E-L* stage 2 (“Bud scales opening”) and stage 3 (“Wooly bud with or without green showing”), while Crimson Pearl and Petite Pearl ranged from stage 1 (“Winter bud”) to stage 3 and stage 2, respectively. Given the current weather forecasts for relatively cool temperatures, budburst (E-L stage 4) could be more than another week away for the earliest varieties. However, this very early spring puts all the cultivars’ development ahead of this time last year and in 2019. At the Peninsular Agricultural Research Station (PARS), all varieties are still at E-L stage 1 (“winter bud”).

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Pests

No pests or disease have been noted.

Growing Degree-Day (GDD) Accumulations

Depicted in Figure 1 and Table 1 are the GDD accumulations from April 1 to April 13 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.

Currently at WMARS, the 2021 season is very early with more than twice the GDD accumulation than in either the 2020 or 2019 seasons, at this time. The current GDD accumulation at PARS is similar to what WMARS experienced in 2020 and 2019.

Table 1. Growing degree day accumulation as of April 13, 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	104	31	32
PARS	36	1	5

*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.