Weed control is the No. 1 challenge for U.S. grain sorghum producers who do not have the luxury of genetically modified hybrids that allow non-selective, post-emergence, over-the-top herbicide use to control numerous weeds that compete with the crop and reduce grain quality.

That may change. Kassim Al-Khatib, Kansas State University, says herbicide resistant, non-GMO sorghum hybrids could be as close as 2011, depending on EPA clearance.

Khatib, speaking at the Texas Plant Protection Association in College Station, Texas, said sorghum growers need new technology to control weeds. “That’s their No. 1 need, higher than breeding, disease and insect control."

“Poor weed control is a consistent issue, especially with no-till systems since cultivation is not an option.” Growers have fewer options since the weeds and grasses they need to control may be similar to sorghum. Also, much of the prime sorghum production region – Texas, Oklahoma and Kansas – plants without irrigation and with limited soil moisture soil-applied herbicide activity may be compromised.

“Post emergence herbicides do not provide the broad spectrum weed control we want and some may injure sorghum,” Khatib said.

“We need to find new options for post emergence treatment for grass control,” he said. “So we began a project in 2003 to search for herbicide resistant genes in wild sorghums.”

He said the effort included seeking out resistance to two different kinds of herbicides, ALS- and ACC-inhibiting types. ALS herbicides include Glean, Accent, Resolve, Staple and Steadfast. The ACC products include Assure II, Fusillade, Post, and Select.

“Resistance for each of these herbicide classes will bring different values,” Khatib said.

“We searched for ALS-inhibiting herbicide resistance in populations of shatter cane, where we know we have resistance. We found one population with high ALS resistance and resistance to several ALS chemistries.”

Researchers used those shattercane selections to back cross with elite sorghum hybrids to develop plants with a high level of ALS resistance.

“Level of resistance is extremely high,” Khatib said. “We have sequenced the gene to determine the level of resistance.” Goal is to identify cross resistance to all ALS compounds, he said.

Materials used on the ALS resistant sorghums should show good broadleaf and grass control with post emergence activity. They also permit crop rotation flexibility. “Also, several available herbicides provide alternatives for growers and some are low risk materials. It’s a cost effective program for both seed and chemical expenses.”

Khatib said the major weakness of the new resistant hybrids includes some weed resistance to ALS herbicides and the chemistry is weak on some grasses.

The search for ACC-inhibiting resistance also included screening wild sorghums. “We identified a resistant gene in Sudangrass. Resistance is strong and is a single gene. We back-crossed to elite lines of sorghum and found exceptional resistance.”

Again, they sequenced the gene and found mutations with ALS resistance. “But if the plant is resistant to everything we can’t kill volunteer sorghum,” Khatib said. “We developed one that is susceptible to one and resistant to the other.”

He said strong points for the AC-resistant hybrids include ability to use post emergent herbicides that are effective, offer flexible rotation options and are cost effective.

Weaknesses include lack of activity on broadleaf weeds, no soil residual, and potential for ACC-resistance to develop.

“We are in the process of evaluating the technology. We see great potential for both the ACC and ALS resistance.”

Availability is close. He said three sets of ALS resistant sorghum materials were released in 2007 and 2009. In the fall of 2007 they released 34 sets of ALS resistant sorghum “for development.

“Almost all of the seed companies are incorporating these traits into grain and forage sorghums,” Khatib said. “The IR-4 program will conduct research to register Assure II in sorghum. We expect a package in 2010 and it will probably be 2012 before we can get a state label. The seed is ready. We have enough to market by 201, maybe 2011 with a Section 18.

“I think grower acceptance of this technology will be high. They currently have no good post emergence grass materials and the ALS and ACC technology offers a good opportunity to control grass and broadleaf weeds.

‘We’re also working on a stewardship program, which could be separate hybrids.”

email: rsmith@farmpress.com