Agronomy •  2023-05-10

How does weed pressure impact corn and soybean yield?

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Corn and soybean crops are both sensitive to early weed competition. The higher the weed pressure, the higher the risk of yield loss.

Weeds that emerge before or at the same time as corn or soybeans are the most competitive and present the greatest risk to yield loss. Peter Sikkema, Professor, Field Crop Weed Management at the University of Guelph says research has shown that delaying herbicide applications in corn can result in yield losses of 1-3.5 bu/ac. per day.

Delaying weed control applications in corn and soybeans can have a serious economic impact, making timely herbicide applications essential to your weed management strategy. A two-pass weed control strategy – applying an effective pre-emergence herbicide followed by a post herbicide to clean up any weed escapes – offers corn and soybeans their best start.

Problematic weeds can be especially harmful to corn and soybean yields. Glyphosate-resistant weeds, like Canada fleabane and waterhemp are becoming an increasing concern for farmers. You can’t ignore the impact of the humble lamb’s-quarters either, it’s the most prevalent broadleaf weed in Eastern Canada. According to the Agronomy Guide for Field Crops, Publication 811, lamb’s-quarters can cause a 30-40% yield loss at densities as low as 5/sq m2.

Tips for preventing yield loss:

  • Plan for a two-pass weed control system. This weed management program delivers the best control option and return on investment (by reducing yield loss) for corn and soybeans.
  • Spray early. Weeds are easier to control when they are small, and removing weeds early minimizes crop interference and competition for resources like moisture and sunlight.
  • Choose multiple effective modes of action. Add diversity to your weed control program to achieve better results and delay herbicide resistance by adding different effective modes of action and herbicides with residual to your tank. This weed control program approach will help keep weeds off balance and preserve application options for future years.