Early season weeds in corn not only compete and reduce yield, but mean more nitrogen fertilizer is required to maintain good yields. Many farmers recognize that today’s herbicides can provide excellent control – and some can control weeds at advanced stages. The tendency may be to delay applications so one application of herbicide gets all the weeds. But studies in Wisconsin and demonstrations in Manitoba show that even though weed control may be 100% in such fields, the nitrogen efficiency is much reduced. Wisconsin studies showed that compared to weed-free fields, when control was delayed until weeds were 4” and 12” tall, an extra 20 to 60 and 60 to 160 lb N/ac respectively was required for full yield. So to optimize nitrogen efficiency in corn, control weeds early.
Submitted by: John Heard, Crop Nutrition Specialist, MAFRD