End of Season Rainfall and Temperature Summary

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

All corn fields planted between mid-April and late May should have accumulated enough growing degree days to reach blacklayer at this point. Mid-April corn should have reached blacklayer the last week of August, while late May plantings should have only needed 7-10 days longer. The colder weather in late April and Early May (Figure 1) slowed down early accumulation of heat units so that late May planting wasn’t too far behind. We saw a similar event in 2019 (https://sites.udel.edu/weeklycropupdate/?p=14264), with the second week of May having temperatures in the low 40s. This year, we had very large fluctuations in temperature in April and May, with steady, but hot temperatures throughout July during pollination (Figure 1).

Figure 1. Average daily temperature during the corn growing season for the three Delaware counties.

We had more consistent rainfall in 2019 as well, with a lack of precipitation not occurring until the second week of June (https://sites.udel.edu/weeklycropupdate/?p=14264). This year, our Newark research farm received no rainfall between late May and late June, and only caught up to last year’s total with the rainfall in late August (Figure 2). The worst drought period in Sussex occurred in early July, when many fields were starting to pollinate. Both Sussex and New Castle county sites accumulated 22 inches of rainfall between April and September 15th, but it was lacking during critical early growth stages of corn and soybeans, so fields without irrigation may suffer. The bright side is that many storms bypass Georgetown altogether, so many fields may have been luckier than us. Between April 15 and September 15th, Kent County (Dover AFB) received 32 inches of rain, with a large portion occurring during the tropical storm. So although the total is high, it is unlikely much of it infiltrated our soils, and either ponded or ran off the fields. Good luck with your corn harvest!

Figure 2. Season-long rainfall accumulation for the three Delaware counties.