Herbicide-Tolerant Milo Arrives

ROCKVILLE, MD. (DTN) -- After a long wait, sorghum growers will have three herbicide-tolerant hybrid options coming onto the market for the 2021 season.

All three are non-GM (genetically modified) technology. Two of the sorghum lines -- igrowth hybrids from Advanta and Inzen hybrids from Corteva -- can tolerate applications of certain labeled Group 2 ALS-inhibitor herbicides: Zest WDG (sulfonylurea) for Inzen and ImiFlex (imidazolinone) for igrowth hybrids.

The third system, Double Team hybrids from S&W, tolerates applications of a labeled Group 1 ACCase-inhibitor herbicide called FirstAct (quizalofop).

There are other key differences among the traits in availability, corresponding herbicides, existing weed resistance concerns and stewardship requirements.

DTN talked to Brent Bean, director of agronomy for the United Sorghum Checkoff Program, and Josh McGinty, an Extension agronomist at Texas A&M, to unpack these details and answer some questions.

CHART BREAKDOWN OF THE TRAITS

PRODUCT	HERBICIDE TOLERANCE	HERBICIDE PARTNER	WEED TARGET	RESID-UALACTIVTY	SPRAY TIMING	REG. STATUS	PLANTBACK REQ
igrowth from AdvantaAlta Seeds	ALS-tolerant (Group 2), specifically imidazolinones	ImiFlex1 from UPL(imazamox)	Broadleaf and grasses	Yes	Pre and post	Trait and herbicide approved for use in the U.S.	No sorghum planting for 18 months after use
Inzen from CortevaPioneer	ALS-tolerant(Group 2),specifically sulfonylureas	Zest WDG2 from Corteva (nicosulfuron)	Grasses only	No	Post only	Trait and herbicide approved for use in the U.S.	No sorghum planting for 18 months after use
DoubleTeam from S&W Sorghum Partners	ACCase-tolerant(Group 1)specifically fops group	FirstAct3 from ADAMA (quizalofop)	Grasses only	No	Post only	Trait and herbicide approved for use in the U.S., but no Canadian export approval as of 3-17-21	No sorghum planting for 4 months after use

For a downloadable version of this chart, click here: https://www.dtn.com/…

1 ImiFlex label: http://www.cdms.net/…

2 Zest WDG label: http://www.cdms.net/…

3 FirstAct label: http://www.cdms.net/…

WHAT IS AVAILABLE IN 2021?

For 2021, only the igrowth sorghum hybrids will be widely available, Bean noted. Advanta is selling five of these hybrids under its Alta Seeds brand, in medium early to medium maturity groups, with plans to expand those maturity groups even further in the coming years. See more here: http://altaseeds.advantaus.com/….

Inzen hybrids will be in shorter supply. Corteva is making an "introductory supply" of hybrids available under its Pioneer brand this spring, with the goal of a full commercial launch in 2022. See the company's news release here: https://www.pioneer.com/….

Double Team hybrids are also in limited supply, with S&W offering a "limited launch" of three Sorghum Partners hybrids that range from very early to medium maturity. See the company's news release here: https://www.prnewswire.com/….

ARE THERE WEED RESISTANCE CONCERNS?

None of these technologies is a one-herbicide solution to weed problems in sorghum, Bean and McGinty stressed. They can all help with grass control in sorghum -- and one can help with broadleaf control, too -- but they are not new chemicals, and resistant weeds already exist in the landscape, particularly for the two ALS herbicides, Zest WDG and ImiFlex.

"At the end of the day, those two herbicides are ALS herbicides, and we've used this class of herbicides for a long time, and there are a lot of ALS-resistant weed issues across the country," McGinty cautioned. "So, stewardship is something we need to keep in mind."

Remember that a weed that is resistant to one kind of ALS herbicide is likely to tolerate other herbicides in the class, Bean said. "So, if you have a sulfonylurea-tolerant grass, it could well be tolerant to imidazolinones, too," he explained. "And if growers can't control their grasses with an ALS herbicide in other crops, they need to be aware that it will be an issue in sorghum, too."

ACCase-resistant weeds are less common in the sorghum cropping system, in part because this class of herbicides hasn't been as widely used there, Bean said. But resistance development is still a possibility.

For all three herbicides, it will be essential to use preemergence applications with residuals such as Group 15 herbicides, spray weeds when they are small, tank mix other modes of action, and scout to find and kill escapes, McGinty said.

"None of these sorghum herbicides will do to a grass what glyphosate would," he cautioned. "You have to be on your A game and spray at the right size, or things will get of control very quickly."

WHAT SORT OF STEWARDSHIP IS REQUIRED?

All the new herbicide-tolerant sorghum hybrids have full U.S. regulatory approval, but the DoubleTeam system is still waiting on import approval from Canada, expected later this year. Until then, any grain from these hybrids must be funneled to local markets and kept out of the export channel, Bean said.

For all three sorghum technologies, another kind of stewardship is required: Growers need to prevent cross-pollination of the traited sorghum hybrids with genetically similar grass weed species, such as shattercane and johnsongrass.

These are two major weeds of many crops and transferring herbicide-resistant genes from these new sorghum varieties into them would be a blow to weed-control efforts and the longevity of these traits, Bean and McGinty stressed.

That's why the labels of the two ALS herbicides, Zest WDG and ImiFlex, require crop rotation away from sorghum to another crop in the year following their use. That way, if weeds with ALS-tolerance or weeds that have cross-pollinated with the traited sorghum survive, growers have a chance to clean them up in a different crop system the next year, Bean explained.

The ACCase-herbicide, FirstAct, doesn't have this rotation requirement, but both Bean and McGinty said they hoped growers consider rotation anyway, to help preserve the technology.

Keep in mind these additional stewardship recommendations Bean recommends to limit gene flow from traited sorghum into weeds:

-- Control johnsongrass and shattercane plants in your fields, ditches, fence rows, and other areas near your field so that flowering does not coincide with the herbicide-tolerant sorghum, to limit the risk of outcrossing and gene flow.

-- Control volunteer sorghum and sorghum off-types prior to flowering.

-- Consider using a desiccant at harvest time to dry down the crop and halt weed seed production of weed escapes.

-- Avoid spills along roadsides during harvest and consider tarping trucks to avoid dropping seed that could grow and later cross-pollinate with johnsongrass and shattercane.

-- If you have johnsongrass or shattercane weed populations in your field with resistance to any of the herbicides in these new technologies, don't use that particular herbicide-tolerant technology.

See a Sorghum Checkoff presentation on the three different technologies, including some weed control field testing, from Bean here: https://www.sorghumcheckoff.com/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow her on Twitter @Emily_Unglesbee

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