Acetolactate synthase inhibiting herbicides have been used to control grass weeds in crop production such as corn, cotton, soybeans and wheat, but only recently has this technology been available in grain sorghum, a Texas A&;M AgriLife Extension Service specialist said.
Better known as ALS-tolerant herbicides, Dr. Jourdan Bell, AgriLife Extension agronomist in Amarillo, is part of a larger study encompassing other areas of Texas as well as neighboring states to test the effectiveness of the DuPont herbicide Zest and Pioneer ALS-resistant grain sorghum.
"It's very important that we are involved in these trials because we are working to provide unbiased results directly to our local producers regarding successful weed control with this technology, Bell said.
"As our farmers look at their bottom line and analyze their inputs, it's very important that they understand the ideal crop stage and proper rates at which to apply the herbicides in order to achieve optimal herbicide performance.
Historically controlling grassy weeds in grain sorghum has not been possible because it is a grass-based crop; herbicides used to treat grassy weeds would also kill the sorghum, Bell said.
A side-by-side comparison of treatments in the ALS-tolerant herbicide study in Randall County. (Texas A&;M AgriLife Extension Service photo by Dr. Jourdan Bell)
"The ALS-tolerant gene was actually located by Kansas State in shattercane and released to private breeding companies. Through natural breeding, it has been incorporated into several grain sorghum varieties that are currently in research and development with Pioneer and Advanta Seeds, she said.
In her study located northwest of Canyon, she is evaluating the ALS herbicide Zest, which is a new formulation of nicosulfuron herbicide labeled by DuPont, with the assistance of Dr. J. D. Ragland, AgriLife Extension agriculture and natural resources agent in Randall County.
"We're looking at different rates of that herbicide, tank mixes and growth stages to control Johnsongrass in grain sorghum, Bell said. "Of course, grassy weeds, just like any weed, can be a significant problem for crop production because they're competing for water, nutrients and even light.
Zest will be labeled to control grassy weeds, including shattercane, volunteer wheat, volunteer grain sorghum, barnyard grass, foxtail and even Johnsongrass, she said.
"It is critical that we look at the timing of the herbicide application not only for the crop but also the size of the weed, Bell said. "We are looking at a grassy weed that is generally 2 to 4 inches tall. We are not going in as a rescue treatment trying to control 3 to 4 feet tall grassy weed species.
In the trial, they made two seasonal applications of the Zest herbicide: a 12-ounces-per-acre treatment and then a second treatment one month later to control a second flush Johnsongrass in the plots.
"We have seen that it is critical to include a pre-emergent herbicide and follow up with a post broadleaf herbicide in the Zest tank mix because the Zest herbicide is only controlling the grassy weed species, Bell said.
This trial is also being repeated in other locations throughout the state of Texas by other AgriLife Extension partners, as well as by Oklahoma and Kansas Extension personnel, she said. Through Extension trials, producers have the opportunity to evaluate the technology and understand the potential uses.
"This is very important so we can see how these herbicides perform under different growing conditions including soils, climate and management practices, Bell said.
She said the results of these Extension-based studies will be used by DuPont Crop Production in their final stages of research and development of the Zest herbicide. It is anticipated that the Zest herbicide will be released along with the ALS-tolerant grain sorghums in 2016.