Richard Taylor, Extension Agronomist; rtaylor@udel.edu
In many areas of Delaware this winter has not only been lacking in significant snow cover but also marginal to deficient in rainfall, resulting in soil moisture levels that are at risk of becoming short as we move to corn planting season in April. Although the forecast does call for rainfall this week, growers who have established cover crops on their 2012 corn fields will need to carefully monitor their soil moisture levels. When spring growth begins, cover crops can remove a large amount of soil moisture in a relatively short space of time. This is not only because of their rapid growth rate in the spring but also because they have a well-developed and often deep root system already established. Cover crops can remove not only surface moisture but the subsoil moisture we often depend on to hold corn during early- to mid-summer drought conditions.
If rainfall between now and early corn planting time remains below normal, growers should think seriously about killing cover crops early, before too much soil moisture is removed. If using a systemic herbicide to kill the cover crop, you should also account for the week to two weeks it will take for the crop to die when determining the timing of herbicide application versus soil moisture levels.
Finally, a number of growers around the state planted the tillage radish or daikon radish as a cover crop this past fall. Although the weather was cold enough on some fields in New Castle County to winter kill the tillage radish, not all fields were completely killed. I suspect that the same is true in the lower counties of Delaware. You should carefully monitor these fields so you can make the decision on whether or not you will need to spray these fields with an herbicide to clean them up in time for corn planting time. Again, you should also monitor the subsoil moisture levels since this crop can send roots very deep into the soil. If it remains alive, a large amount of the subsoil moisture may be lost through transpiration as the radish enters the reproductive stage later this spring.