Cold Climate Grape Cultivar Developmental Stages: April 30, 2020
At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoot development across most cultivars have reached between E-L* stage 3 (“Wooly bud with or without green showing”) with no green showing, while Petite Pearl is between stages 2 (“Bud scales opening”) and 3. Given current weather forecasts budburst (E-L stage 4) could be within another week for the earliest varieties. Similar to last week, grapevine buds are similar to a little behind in phenology to the 2019 season and about a week ahead of 2018.
*E-L stands for the Eichhorn-Lorenz growth stages scale to describe grapevine development.
Petite Pearl E-L 2-“Bud scales opening” 
Crimson Pearl E-L 3 “Wooly Bud” 
Itasca E-L 3 “Wooly Bud” 
Frontenac E-L 3 “Wooly Bud” 
La Crescent E-L 3 “Wooly Bud” 
Brianna E-L 3 “Wooly Bud” 
Marquette E-L 3 “Wooly Bud”
Insect Pests
Grape flea beetles may be feeding on developing buds during this time of the season. As the same as last week, no grape flea beetle has been detected yet at WMARS. There has been minimal pressure of this insect pest at WMARS in the past. However, it is important to scout your vineyard for both grape flea beetles and flea beetle damage as infestations can be localized.
Growing Degree Day (GDD) Accumulations
Depicted are the GDD accumulations from April 1 through April 29 for the past three seasons. Currently, at WMARS, the 2020 season continues to fall between the 2019 and 2018 seasons. 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 (http://newa.cornell.edu/index.php?page=about-degree-days).
Growing degree day accumulation as of April 29, 2020 (April 1 biofix date; base 50 °F BE*);*BE = Baskerville-Emin calculation method
| Location | 2020 | 2019 | 2018 |
| WMARS | 52.3 | 98.6 | 36.1 |
| PARS | 6.6 | 20.7 | 9.2 |