Grape Cultivar Developmental Stages: June 12, 2020
Phenology
At the West Madison Agricultural Research Station (WMARS) in Madison, WI, shoot development as of June 11 ranged between E-L* stage 18 (“Flower caps still in place”) on many Petite Pearl to some shoots at stage 26 (“Cap-fall complete”) on Brianna, Frontenac, and Marquette. It is interesting to note Brianna advanced the most over the past two weeks, from being one of the later developed cultivars to one of the most advanced. As the flower caps are pushed off, the pollen-bearing stamen extend and then eventually fall off, with hopefully great fruit set to come!
BR: E-L25 to 26 “80% caps off to Cap-fall complete” 
CP: E-L21 to 23 “30 to 50% caps off” 
FR: E-L23 to 26 “50% caps off to Cap-fall complete” 
IT: E-L21 to 23 “30 to 50% caps off” 
LT: E-L23 to 25 “50 to 80% caps off” 
PP: E-L18 to 20 “Flower caps still in place to 10% caps off”
*E-L stands for the Eichhorn-Lorenz growth stages scale to describe grapevine development.
Growing Degree Day (GDD) Accumulations
Depicted in the table and on the graph are the GDD accumulations from April 1 through June 10* for this season and the past two seasons. Currently at WMARS, the GDD accumulation for the 2020 season continues to be similar to the 2019 season. In comparison, in 2018 the early June heat accumulation was not much different from we have been experiencing (note that the graph lines during this period are generally parallel), but that the higher GDD total is from the increase in heat accumulation during most of May of that year. At the Peninsular Agricultural Research Station (PARS), the GDD accumulation so far this year continues to be in between what was reached in 2019 and 2018.
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 June 10*, 2020 (April 1 biofix date; base 50 °F BE**) at the WMARS and the Peninsular Agricultural Research Station (PARS).
| Location | 2020 | 2019 | 2018 |
| WMARS | 542.1 | 493.7 | 668.0 |
| PARS | 292.2 | 217.3 | 346.7 |
*GDDs presented here are for one day earlier than the E-L stage phenology, due to NEWA model outage.
**BE = Baskerville-Emin calculation method
Accumulation of growing degree days (GDD) as of June 10 (April 1 biofix date) at both WMARS and PARS for 2018, 2019, and 2020.
This article was posted in Grapes and tagged grape phenology, Grapes, grapes developmental stages.