According to data from the last two years (https://sites.udel.edu/agronomy/2020/09/23/2019-2020-corn-growing-degree-days/), silking and pollination (R1) has occurred between 1320 and 1594 growing degree days, while VT (tasseling) occurs between 1200-1300. 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.
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Delaware Agronomy Blog
University of Delaware Cooperative Extension
Category: Weather (page 2 of 3)
Emerging corn in a rye cover crop
While it may not seem much warmer than it was in 2020, having steady days above 50°F had provided much faster emergence than last year. In 2019 we were getting about 10 growing degree days (GDD) per day, while now we are seeing 15-20. The threshold for emergence is about 100-120 GDD, which we have reached for most fields planted between April 15 and April 22nd (Table 1). In 2020, we had only reached half of that (60-90 statewide) over the same time period.
The standard method used to follow and predict corn growth stages is using growing degree days (GDD). This is a calculation that uses average daily temperatures to measure accumulated heat over the growing season. Most of the GDD values we use are from the Mid-West, so we have followed a few research fields the past two years to compare how DE lines up. We have also included days from planting and light accumulation (pulled from DEOS) to compare other measurement methods (Table 1 – flip phone sideways for best presentation).
| Table 1: Following Corn Vegetative Growth Stages (2019-2020) | ||||||
| Emerge | V3 | V6 | V9 | V12 | VT | |
| Days from Planting | 5-13 | 12-31 | 22-48 | 35-63 | 44-76 | 53-82 |
| Growing Degree Days | 84-150 | 219-310 | 492-603 | 787-950 | 1001-1337 | 1231-1322 |
| Total Light | 125-302 | 271-609 | 530-996 | 828-1343 | 1055-1664 | 1265-1508 |
The preferred soil temperature for corn germination is 50°F, which allows the seed to begin root and shoot growth. When soils fall below this temperature, germination may be limited and seeds may rot in the ground. Many of the weather stations on DEOS (http://www.deos.udel.edu/) have soil temperature as an option, so you can track current conditions. Continue reading
Since the rainfall this weekend, cooler temperatures have slowed the accumulation of growing degree days. Since April 14th we had observed a steady trend in GDD accumulation, keeping emergence on track between 7-10 days. Any planting done since May 6th may see delayed emergence, compared to previously planted fields. For those fields planted mid-April you may be at V4-V5. As temperatures warm back up, be prepared to sidedress between V6-V8.
Figure 1: Growing degree days in the Dover area since April 14th.
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