UNL CropWatch April 22, 2011 Weed Scout Update: Summer Annuals Now Emerging

UNL CropWatch April 22, 2011 Weed Scout Update: Summer Annuals Now Emerging

April 22, 2011

Giant Ragweed


Giant ragweed (Ambrosia trifida) seedlings germinating in soybean residue in Richardson and Nemaha counties in southeast Nebraska (April 16).

Summer annuals, such as giant ragweed, are emerging and growers should be scouting fields in southeast Nebraska.

Giant ragweed has round to spatulate shaped cotyledons and the first true leaves may appear unlobed to tri-lobed.

Winter annual weeds are the most obvious weeds currently present in no-till fields because they are large and starting to flower; however, many summer annual weeds have started emerging, including giant ragweed, common lambsquarters, and velvetleaf. In surrounding states populations of giant ragweed have developed resistance to glyphosate.

Plan Treatment to Avoid Resistance

If you scout and find giant ragweed in your field prior to corn or soybean planting, using a second effective herbicide mode of action with glyphosate in a burndown/preemergence herbicide application is recommended. Selecting effective herbicides in place of or in addition to glyphosate will reduce the potential for glyphosate-resistant populations developing in your field.

More Information

Detailed information about giant ragweed can be found in the Glyphosate, Weeds, Crops publication Biology and Management of Giant Ragweed.

Additionally, options for herbicide control can be found in the corn and soybean sections of the 2011 Guide for Weed Management in Nebraska.

Lowell Sandell
Weed Science Extension Educator, Lincoln