Phenology

At the West Madison Agricultural Research Station (WMARS) in Verona, WI, shoot development across all cultivars has reached at least E-L* Stage 3 (“Wooly bud with green showing”) (Table 1). Petite Pearl vines have many buds still at Stage 2 (“Bud scales opening”), while La Crescent and Marquette vines have some buds that have reached bud burst, Stage 4 (“Bud burst, leaf tips visible”). The temperatures this weekend (May 1-2) will be warm, which may lead to other cultivars reaching budburst, but cooler temperatures into next week could mean substantial development may be more than another week away. The recent cooler weather has slowed all the cultivars’ development, making it more comparable to this time in 2019.

Table 1. Phenology and development of cold climate interspecific hybrid grape cultivars at the West Madison Agricultural Research Station in Verona, WI, as of April 28, 2021.

Cultivar	E-L Stage*	Description
Brianna	3	Wooly bud ± green showing
Crimson Pearl	3
Frontenac	3
Itasca	3
La Crescent	3-4	Wooly bud ± green showing to Bud burst, leaf tips visible
Marquette	3-4
Petite Pearl	2-3	Bud scales opening to Wooly bud ± green showing

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Growing Degree-Day (GDD) Accumulations

Depicted in Figure 1 and Table 2 are the GDD accumulations from April 1 to April 28 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).

Currently at WMARS, the 2021 season GDD accumulation has slowed over the last two weeks, resulting in a total comparable to this time in 2019. The GDD accumulations as of April 28 at PARS for this season and the previous two range from a low of 7 GDDs in 2020 to 34 GDDs for 2021.

Table 2. Growing degree day accumulation as of April 28, 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	115	51	99
PARS	34	7	21

*BE = Baskerville-Emin calculation method

Figure 1. Accumulation of growing degree days (GDD) as of April 28 (April 1 biofix date) at both the West Madison Agricultural Research Station (WMARS) and the Peninsular Agricultural Research Station (PARS) for 2019, 2020 and 2021.

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