Eastern grape leafhopper, Erythroneura comes (Say), is an important pest of grapes in the eastern half of the United States, capable of causing reductions in the quality and quantity of the crop. I investigated the phenology (i.e., seasonal development) of this insect using a growing degree-day (GDD) model. Growing degree days were calculated above a lower developmental threshold of 10°C (50°F) using the single sine wave method. Leafhopper nymphs were counted weekly on grape leaves from 2016 to 2018 at a vineyard in Perkins, OK. Differential abundance was observed across eight cultivars: Cynthiana, Chambourcin, Chardonel, Frontenac-Gris, Niagara, Noiret, Rubaiyat, and Traminette. The cultivars Noiret and Traminette had the highest abundance of nymphs, while Niagara and Cynthiana had the lowest abundance. In 2016, there were three peaks in population abundance, indicating three separate generations of the insect, while in 2017, there were three and possibly a partial fourth generation. In 2018, three peaks occurred. I report and discuss degree day calculations for generational peaks, as well as establish GDD-based recommendations for monitoring practices for this leafhopper in Oklahoma vineyards. The presence of the leafhoppers Erythroneura ziczac Walsh and Empoasca fabae (Harris) is also reported.