Weeds to Watch: Common waterhemp
Glyphosate-resistant common waterhemp was first identified in northwest Missouri in 2006 where weed scientists found plants surviving up to eight times the labeled rate. In the past two years Kansas, Illinois and Minnesota have also confirmed glyphosate-resistant populations.
A recent survey of Missouri retailers conducted by the University of Missouri and Syngenta Crop Protection gauged the perceived level of glyphosate-resistant waterhemp in soybeans throughout the state. The results represent over 30 percent of the total Missouri soybean growing area for 2007, or about 1.4 million acres. For specific results from the survey view the bulletin.
Unlike self-pollinating species, waterhemp is a dioecious, or cross-pollinating, species with separate male and female plants making it more likely to develop herbicide resistance. It is likely that resistant genes are moved across the farming landscape via pollen. Common waterhemp is a prolific seed producer and has an extended germination and emergence period throughout the season.
An effective weed management plan requires more than a single year strategy. Recently, Aaron Hager, weed scientist at the University of Illinois, developed steps to waterhemp management.
· Step 1. Apply a full rate of a soil-residual herbicide no sooner than 7 days before planting or no later than 3 days after planting.
· Step 2. The initial postemergence application of glyphosate must be made when waterhemp is 3 to 5 inches tall.
· Step 3. Fields must be scouted 7 days after the initial glyphosate application to determine treatment effectiveness.
· Step 4. If waterhemp control is inadequate and retreatment is necessary, consider applying a PPO-inhibiting herbicide at a full labeled rate (with recommended additives) as soon as possible.
· Step 5: Rescout the treated field within 10 to 14 days to determine effectiveness of the PPO-inhibiting herbicide treatment. If scouting reveals that plants treated with a second herbicide application might survive, implement whatever tactics are available or feasible to rogue these surviving plants from the field before they reach a reproductive growth stage.
For more information about glyphosate-resistant waterhemp, click on a link below:
· Glyphosate-Resistant Waterhemp Estimated on 200,000 Acres in Missouri
· Recommendations for Management of Glyphosate-Resistant Waterhemp in Illinois Soybean