Want to make sure your corn crop makes the best use of all the nitrogen (N) it can? Then you’d better control weeds early, say experts from Minnesota and Wisconsin.

“Early season yield loss is due largely to weeds that sequester about 30-45 lbs. of N/acre out of the field from planting time up until about the end of June,” says Jeff Gunsolus, University of Minnesota Extension weed scientist. “You don’t get that N back during the season after your weeds are controlled. So, it’s much better to kill the weeds early than to be in the situation where you need to add more N to a field where weeds have sequestered it.”

Early weeds consume a costly amount of N out of the soil, and farmers may be unable to compensate for that nutrient loss by adding additional N later, agrees Carrie Laboski, University of Wisconsin Extension soil scientist. “The bottom line on our two-year study is that N fertilizer is more efficiently used when weeds are controlled pre-emergence or at a 4-in. weed height compared to waiting until weeds are 12 in. tall,” she says. “The economic return on your investment in N fertilizer and herbicide is maximized when weeds are controlled early.”  


January 2011