Early weeds vs. late weeds

Gordon Vail

The cost of early-season weed competition in corn has been well documented. But how do you know what “early-season weeds” are?

Depending on your location, weeds start emerging as soon as it’s warm enough for their seeds to germinate. And flushes of weeds can show up all season long. “Early-season” usually refers to the life of the crop, rather than a specific time of year.

The weeds that emerge about the same time as the crop compete the most with your corn for nutrients, water and light. For example, one giant ragweed can beat 12 corn plants for nitrogen.

Pre-emergence residual herbicides help control these early weeds and protect yield potential.

Researchers like Clarence Swanton of the University of Guelph, Ontario, define early weeds as those that emerge with the corn. So while in-season applications are important to manage weeds for next year, controlling weeds before or soon after they emerge is the best way to protect yield this season.