One current recommendation is to begin planting corn when soil temperatures are in the high 40s and the short-term forecast calls for warm days that will continue pushing soil temperatures higher. If soil temperatures are in the high 40s and the weather forecast calls for cold wet conditions within the next 48 hours, soil temperatures will likely drop and planting should be delayed until temperatures warm.

That recommendation is simply not our experience in Wisconsin and likely the northern tier of U.S. states. If we waited until soil temperatures were above 40° F we would need to wait until May in many years (Figure 2). It only gets later as we move north. Yet, our highest yielding planting date are in late April and early May.

Figure 2. Last date when the minimum soil temperature at the two-inch depth was above 40° F at Arlington, WI.

The only time I thought our UW Corn Hybrid Trial plots had been affected by imbibitional chilling was during 2006 at Seymour, WI (Figure 3). I happened to be along on that planting trip. It began to snow after we had finished planting and continued to be cool and wet for the next 72 hrs. We went back to the field a few weeks later and unbeknownst to us at planting, found that the field had shallow swales and a drainfield. Corn emergence was perfect over the drainfield and on the ridges of the swales. However, much plant death occurred between the drainfield spurs and swale depressions. We did not observe standing water, although it could have been another possible reason for plant death. We abandoned the trial due to stand variability.