Growing Degree Days (GDD) and Rainfall Through August 28th

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

If spring weather caused you to plant fields spaced out from April to June, you may get a good idea of what the weather can do to a crop. Considering the varying planting dates, flooding, drought, and high temperatures, we have about three years’ worth of weather in one summer to observe the effects on growth, pollination, and kernel abortion.

Most later planted fields (mid-June) probably saw decent temperatures and rainfall for pollination, while earlier planted fields may have more tipback during the mid-July heatwave. Kernels forming under stress may also abort, which could certainly be seen with temperatures above 90 the week of August 17^th and our current heat wave. Still, nighttime temperatures have often been below 72°F, so that should help.

Looking at GDD, any fields planted in April (that survived) should be starting or at blacklayer. Most fields planted in May across the state should be starting or full within R5 (dent). The only way you can be sure is to walk out and check your corn.

R1 (Silking): 1400 GDD
R2 (Blister): 1660 GDD
R4 (Dough): 1925 GDD
R5 (Dent): 2190-2450
R6 (Blacklayer): 2700

Table 1: Accumulated growing degree days based on planting dates through August 28^th.

We still cannot complain about rainfall too much. There have been a few storms popping up across the state, enough that dryland should have received a little moisture. Since mid-August, we have received less than an inch in most parts of the state, and the heat this week will probably stress corn and beans.