At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoot development ranged between E-L* stage 3 (“Wooly bud without green showing”) on Petite Pearl to a few buds at stage 5 (“rosette of leaf tips visible/advanced budburst”) on La Crescent. Itasca and Frontenac buds and most La Crescent were at stage 4 (“wooly bud with green tips showing/initial bud burst”). Brianna, Crimson Pearl, and Marquette buds were at a mix of stages 3 and 4. Currently the bud phenology is behind about one week that experienced in 2019, and in 2018, most cultivars were at E-L stage 7 (“first leaf separated from shoot tip”).

Although overwintering injury is not expected to be significant this year, in a week or two after budburst it will be important to look at the shoots of your vines to see which buds have ‘pushed’ from either primary (typically more fruitful), secondary (less fruitful), or tertiary (no fruit) buds, in order to assess ultimate damage and potential yield.

The minimum air temperature recorded by the NEWA weather station at WMARS for the early morning of May 9 was 29.7 °F. No damage was seen on any of the new bud growth.

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

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Pests

Only two buds showed any signs of grape flea beetle or cutworm damage at WMARS since the last report. It is important to scout your vineyard for both grape flea beetles and cutworm and their resulting damage, as infestations can be localized. For more information on this, please see Christelle Guédot’s grape insect scouting report.

Growing Degree Day (GDD) Accumulations

Depicted are the GDD accumulations from April 1 through May 13 for the past three seasons. Currently at WMARS, the 2020 season is less than, but closer to the 2019 season in heat accumulation, and has become much less than the 2018 season. 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.

Growing degree day accumulation as of May 13, 2020 (April 1 biofix date; base 50 °F BE*) at the WMARS and the Peninsular Agricultural Research Station (PARS).

Location	2020	2019	2018
WMARS	104.5	129.7	190.9
PARS	27.8	34.8	67.6

*BE = Baskerville-Emin calculation method

This article was posted in Grapes and tagged cold climate grapes, grape phenology, Grapes, WFN.