Richard Taylor, Extension Agronomist; rtaylor@udel.edu
With the recent heat, corn development has been proceeding rapidly and before the corn develops past the point where you can get into the field to treat for the most common micronutrient deficiencies we see in Delaware fields you or your consultant-scout should check your most developed corn fields. Pay particular attention to fields that have had a history of micronutrient problems in corn and small grains and in fields where the soil pH is close to neutral (pH of 7.0). Many fields in Delaware begin to show manganese (Mn) deficiency as our soil pH rises towards neutral or alkaline. Application of even a ¼ of a pound of actual Mn per acre up to 1 or 2 lbs/acre in with a post-emergence weed control spray often will restore plant vigor. Mn deficiency in corn like most micronutrients shows up as an interveinal chlorosis meaning the parallel veins remain green and the tissue in between the veins turns yellow to white. The symptoms occur first on the newest growth since the plant is unable to take Mn from older tissue (the first leaves to appear and that will die soon anyway) and move it to the newly developing leaves and ears. The fact that corn is setting its ultimate yield potential even as early as the fifth leaf stage is something we often forget. Micronutrient deficiencies during this early vegetative growth will certainly reduce yields since the active growing points, such as the developing ear, are the first to suffer from a deficiency since micronutrients are not mobile in the plant.