Shedding Light on Yield Loss

It's well documented that weeds taller than 2 inches compete with corn plants for water and nutrients. That's not the whole story to yield loss, however. Just ask Mark Lawson, an agronomic service representative for Syngenta. "The impact of light is much greater than we give it credit for," says Lawson, who has based his own field trials on the research of Clarence Swanton, Ph.D., at the University of Guelph in Ontario.

Swanton's studies have shown that early-emerging corn seedlings contain light-sensing compounds called phytochromes that can detect subtle shifts in the reflected light around them. When weeds emerge with the crop, phytochromes tell the corn seedlings to grow taller stalks and wider leaves to better compete for light. This above-ground growth leaves fewer resources for root growth, which compromises yield potential.

Lawson observed similar results by using inexpensive, green, indoor-outdoor carpet to mimic weeds' effect on corn seedlings. "I've demonstrated a 9-bushel-per-acre yield loss, on average," he says. "It's one more reminder that early-season weed control is vital."