Make a Plan to Stop Ragweed

If you haven’t figured out your weed control strategy for the season it’s time to get it done. Know what weeds are in your field and understand if ragweed—common or giant—is in your soybean fields, it’s especially important to gain control.

According to research at the University of Nebraska, one ragweed plant every 1.6’ of soybean row decreased yield by 76% in 2015 and 40% in 2016. When common ragweed is only 3” apart in the soybean row it reduced yield by 95% and 80% in 2015 and 2016 respectively.

Researchers surmise yield loss was from shading in those years, as water was abundant. The easiest way to control this weed is by destroying the weed seedbank for future seasons. Do this with a no-weed-left-standing threshold.

“Since the ragweed seedbank is short-lived, our research shows it is possible to manage fields infested with giant ragweed by simply eliminating weeds that emerge before they go to seed,” says Jared Goplen, researcher at the University of Minnesota. The University’s research shows a zero-weed threshold reduces the weed seedbank by 96% in just two years.

The same research at UM showed value in moving beyond a corn-soybean rotation. Adding wheat or alfalfa reduced ragweed plants by 38%. Since each plant produces 5,000 seeds, reducing matured plants is critical.

Make sure you scout now and throughout the season. Look for these characteristics to see if your fields have giant ragweed:

• Cotyledon leaves are round, thick and large with purple hypocotyl
• Hairy stems
• True leaves are opposite, three- or five-lobed, hairy, with toothed edges and can be 4” to 8” wide by 6” long
• Small, green flowers, but crop experts urge growers not to let giant ragweed get to the flowering stage.