Observations and reports from Kansas ag retailers indicate that many growers are now using a pre-emergent herbicide prior to kochia emergence in wheat and many more—perhaps a majority—are using a pre-emergent herbicide in addition to glyphosate in Roundup Ready corn and soybeans to control glyphosate-resistant kochia.
It wasn’t until 2011-2012, that the use of pre-emergent herbicide in addition to normal management began to be used effectively in controlling glyphosate-resitant kochia in Kansas, according to Phil Stahlman, a weed scientist based at Kansas State University’s Agricultural Research Center in Hays, Kan.
By 2013, the resistant kochia problem was identified from the Texas High Plains, all the way into the prairie provinces of Canada.” Prior to current pre-emergent herbicide programs, kochia control, by too many wheat farmers, was the use of tillage as part of a control program, K-State weed scientists contend.
“If we till the soil to manage kochia, we’ve lost the conservation gains we made in the last decade or more of using no-till,” Stahlman said.
The researcher is optimistic that kochia is manageable by applying pre-emergent herbicide and dealing with what still comes up later in the growing season.
“Fortunately, the seed life of kochia is relatively short, not more than two to three years. But with uncontrolled kochia on roadsides and fence rows, and if we have one grower in an area who is not on board with how to manage it, it can still be a problem,” Stahlman said.
Stahlman and other researchers are studying the kochia plant’s mechanism of resistance as they look for even better ways to manage the weed and protect crops.
Economics of no-till kochia control
In 2013, then K-State agricultural economist Troy Dumler recognized that the growing resistance of kochia to glyphosate was leading too many producers to consider returning to tillage options for weed control in western Kansas dryland crop rotations.
As early as 2010, Stahlman and a graduate student rated 1,500 wheat stubble fields throughout western Kansas, and found that about 30 percent were tilled in an effort to control the weed.
Long-term data from the K-State Research Center in Tribune, Kan., had indicated there is a significant economic advantage to incorporating no-till practices in a wheat-sorghum-fallow (WSF) rotation, according to Dumler. From 2001-2011, no-till wheat and sorghum yields were approximately eight bushels per acre and 43 bushels per acre higher, respectively, than when using conventional tillage.
Similarly, no-till wheat and sorghum yields were five bushels an acre and 30 bushels an acre higher, respectively, than a reduced-till rotation (conventional tillage prior to wheat and no-till prior to sorghum). The higher yields associated with no-till resulted in a $63 per acre advantage for no-till over reduced-till and an $83 per acre advantage for no-till over conventional-till.
“With the growing difficulty of controlling kochia with a glyphosate-oriented herbicide program, the natural question becomes: How much can be spend on herbicides for kochia control to maintain the economic advantage of no-till?” said Dumler, who now works in private industry.
With assistance from K-State’s weed scientists, he developed an example herbicide budget for kochia control to compare the relative profitability of tillage systems in a WSF rotation to that of a herbicide program that used Round-Up as the primary herbicide option. The results indicate that while herbicide costs nearly doubled for the kochia control program, returns for the no-till rotation were nearly $50 per acre greater than reduced-till and $55 per acre greater than conventional-till. However, the profitability of the no-till rotation decreased by $30 per acre.