Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu; Cory Whaley, Sussex Co. Extension Ag Agent, whaley@udel.edu; Jake Jones, Extension Agriculture Agent, Kent County, jgjones@udel.edu; Dan Severson, Agriculture Agent, New Castle County, severson@udel.edu
At this point last year (Table 1) we had accumulated about 80 growing degree days (GDD) less than we have in 2021 (Table 2), particularly if you had planted by April 15th. The only advantage in temperatures in 2020 was if you planted May 6th, a period which had seen slightly warmer trends compared to this year. One major cause of this trend last year was the cold temperatures from late April to Mid-May (Figure 1), which flattened GDD accumulation in 2020. This year, while there was slower GDD accumulation at the beginning of May, it did not last as long (Figure 1).
| Table 1: 2020 Accumulated Growing Degree Days Based on Planting Date Through May 19th | |||
| Planting Date | New Castle | Kent | Sussex |
| 15-Apr | 159 | 186 | 200 |
| 22-Apr | 159 | 179 | 192 |
| 29-Apr | 157 | 175 | 175 |
| 6-May | 87 | 98 | 94 |
| Table 2: 2021 Accumulated Growing Degree Days Based on Planting Date Through May 17th | |||
| Planting Date | New Castle | Kent | Sussex |
| 15-Apr | 244 | 268 | 278 |
| 22-Apr | 225 | 241 | 254 |
| 29-Apr | 183 | 193 | 207 |
| 6-May | 71 | 69 | 79 |
Figure 1. Accumulated Growing Degree Days in each County Since April 15th in both 2020 and 2021.
Temperatures are not our limiting factor in 2021 for good crop germination and early growth. Instead we are seeing abnormally dry conditions, which has been conducive to field work, but may start limiting crop growth and survival. We have observed little to no rain in the forecast over the next week, which could and will hopefully change. However, there are significantly drier portions of the Delmarva than were observed last year (Figure 2). Volumetric water content was low last year in Sussex County, but this year we are experiencing very dry conditions (Figure 2, darker orange), particularly on the border of Delaware and Caroline County, Maryland. Most of New Castle and the eastern half of Kent had very adequate moisture last year, but now much of Delaware is approaching drought conditions. Topsoil moisture in the upper inch may not be enough to assist with germination, so making sure planter settings are correct is very important. Any field that has irrigation should be maintaining soil moisture as best it can.
We would expect these dry conditions to start to severely decrease good germination. In some cases, fields with high biomass from crop or cover crop residues should benefit field crop production, providing a mulching layer that reduces the loss of moisture to the atmosphere. Combining irrigation with good soil infiltration and reduced evaporation will be beneficial.
Figure 2 Statewide Soil Moisture in Mid-May 2020 and 2021 (USDA/NASA/GMU)