As more growers face resistance issues in their fields, researchers are recommending the addition of residual herbicides for a comprehensive herbicide program.

For optimal resistance management, growers should include a residual herbicide in their weed programs — especially early in the season, either before or at planting, before weeds are emerged and easier to control.

Purdue University Weed Scientist Dr. Bill Johnson warns growers against relying exclusively on post-emerge strategies.

Key findings from Johnson:

• Weeds can start robbing crops of yield when the weeds reach approximately 6 inches in height.

• In post-emerge-only situations, a one-day delay in weed management strategies can result in a 1.2 bushel-per-acre, per-day yield loss in corn, and a one-third of a bushel per acre, per-day yield loss in soybeans.

“By applying a residual herbicide, we can extend the window for putting on a post-emergence herbicide to reduce yield loss and also reduce the exposure of our worst weed problems to glyphosate," Johnson says.