By Chuck Foresman, manager of weed resistance strategies, Syngenta

Glyphosate resistance is a real and growing threat, and is becoming a more personal issue for many growers. Weeds uncontrolled by glyphosate are popping up in greater numbers than ever before. Increased rates and multiple applications are not killing them. Growers are sensing an imbalance to the ease, simplicity and cost effectiveness of glyphosate-tolerant crops.

Across the U.S., 16 states now have confirmed glyphosate-resistant weeds. Of the seven species confirmed resistant to glyphosate, two-thirds have been identified in the last two years, and several more are on the verge.

While weeds such as horseweed have so far proven fairly manageable, recently confirmed glyphosate-resistant giant ragweed and Palmer pigweed are presenting challenges without easy solutions. With Johnsongrass recently confirmed resistant in Argentina, the threat of glyphosate-resistant grass species presents a new concern for U.S. growers.

Each new species brings additional challenges to management programs. In addition, weeds developing multiple resistance to several herbicides or other modes of action are also becoming a reality. Common waterhemp in Missouri also carries resistance to ALS and glyphosate herbicides. In Illinois, a waterhemp population has developed resistance to three different modes of action. Should glyphosate be rendered ineffective there, options for control are extremely limited. In the South, many Palmer pigweed populations are already resistant to ALS-inhibitors, and glyphosate resistance is growing, leaving few and difficult options for control. Along with specific glyphosate-resistance product solutions, Syngenta recommends pre-emergence, residual herbicides on glyphosate-tolerant crop acres and 2-1-2 as a resistance management program for corn and soybean growers - no more than two applications of glyphosate on one field over a two-year period.

Understanding resistance allows growers to proactively develop a management program to delay glyphosate resistance and maintain full yield potential year after year. Knowing the best options available on a field-by-field basis keeps growers one step ahead. For more information on the Syngenta Resistance Management Solutions Module and management options, visit resistancefighter.com.