Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
According to data from the last two years, silking and pollination (R1) has occurred between 1320 and 1594 growing degree days, while VT (tasseling) occurs between 1200-1300 (Table 1). In many of our research fields, VT also began to occur in this range last week, followed quickly by silking.
Stress during pollination can determine initial pollination and kernel set, so temperature becomes very important. Planting date is an important part of this, as corn growth will follow heat accumulation, so cooler springs will take longer to reach R1 and vice versa.
This year many of our fields in Georgetown could have reached silking about July 5th if planted on April 15-April 22, but taken 2-3 days longer every week after that. Fields planted May 15 should start pollination right now, but it will be variety and field management specific. For example, our cover crop trials have had a range in the start of R1 by a few days.
When observing Figure 1, it becomes clear why this is important as a few days in July could add additional stress for pollination. The cooler period during the first week was very conducive to fields already at R1 (planted April 15th), but our highs in the 90s may be causing later planted fields to abort some of their kernels. A lot of this is luck, as a warmer April would lead to earlier R1 stages, but a cooler April could place corn growth at the same stage as May planting. Still, this week is known to be one of the warmest of the summer, so watching your typical days to R1 based on past weather data may give you a better expectation of whether your planting date may hit this warmer milestone.
Table 1. GDD for corn reproductive stages based on 2019-2020 growing seasons
Figure 1. Maximum air temperatures in Georgetown from April 1st to July13th.