Dr. Calvin Trostle, Extension Agronomy/TAMU Dept. of Soil & Crop Sciences, Lubbock, (806) 746-6101, ctrostle@ag.tamu.edu

Finally—Commercially Available Herbicide-Tolerant Grain Sorghums

We have heard about this for years.  In 2022 there will finally be some options for Texas grain sorghum farmers to consider.  Seed for at least some limited acreage of three different herbicide-tolerant grain sorghum hybrids will be available.

These will be best for sorghum farmers that struggle with grass control in grain sorghum.  Grain sorghum itself is a grass, so otherwise this is a tough task.

All three grain sorghum technologies are non-GMO.

• “Inzen” from Corteva/Pioneer
• “igrowth” from Advanta/Alta Seeds
• “Double Team” from S&W Seeds/Sorghum Partners

Here is a short summary of each technology.  Please contact your seed dealer for specific seed availability and further management recommendations.   Two of the technologies are ALS (acetolactate synthase) weed control systems.  (There are several ALS groups including imis, sulfonyls, etc.).  ALS technologies have been used for a long time.  There is resistance among several weeds to ALS.  Do not plant fields with ALS-resistant Johnsongrass or shatter cane.  ALS-resistant Johnsongrass has been confirmed in Texas, to both imidazolinones (imazethapyr) and sulfonylureas (nicosulfuron)(weedscience.org). ACCase technology is acetyl-CoA carboxylase.

Fig. 1.  Grass control (right) by herbicide application in herbicide-tolerant grain sorghum.  (Courtesy Dr. Brent Bean)

Important Criteria for Herbicide-Tolerant Sorghums

• Each has a specific grower stewardship agreement to be signed at purchase. This governs the technology use.  It may include specific guidelines on use, application, etc.
• You must use the designated herbicide, not a similar herbicide with the same active ingredient. There may be slight differences in the formulation that are not known.  Yes, the cost of the designated herbicide is likely higher vs. the same active ingredient in another product.  However, should you have an unexpected level of injury or other issue, then there is no recourse with the company if you have used another product.
• A natural question: Is there any yield data on these three hybrid systems yet in Texas A&M AgriLife testing?  Not yet.  Seed supplies were short in 2021.  None of these herbicide-tolerant technologies were entered in AgriLife Crop Testing trials.  This should change in the near future.  Based on past experience producers should not likely expect these hybrids to be top yielding, though that could come soon.  When many different crop technologies are new to the market—e.g., the first Bt corn hybrids, Roundup-Ready winter canola hybrids, and sugarcane-aphid tolerant hybrids—these were not top yielders.  There was an effort to get the first hybrids out to the growers that needed them the most.  In time, the yield differentials disappeared as the company focused their efforts on including that technology in most of their hybrids.

Inzen (Corteva/Pioneer)

This ALS herbicide program is paired with the nicosulfuron herbicide Zest from Corteva.  It is best used as a postemergence application coupled with an effective broadleaf herbicide following a soil-applied residual herbicide program.  Zest has good activity on grasses, but limited effectiveness on broadleaves.  What is Zest most similar to?—Accent in corn.  As of early December 2021, Pioneer has not yet announced which hybrids will be available for farmers in 2022.  Pollen-mediated gene flow to nearby Johnsongrass and shattercane can increase development of resistance in those weeds.  Control of these nearby weeds is recommended when they are also flowering.  Consult the label for last recommended timing on application for weeds of specific size.  Do not apply to sorghum >20” tall (this serves as the pre-harvest interval).

Based on the supplemental label for reduced crop rotation intervals (CRI) posted at http://www.cdms.net/ldat/ldDEH004.pdf

Selected Zest label rotation restrictions—no soil pH limitations:

• General sorghums, 10 months
• ALS-resistant sorghums, 18 months
• Corn, anytime
• Cotton, 10 months
• Winter small grains (wheat, oats, rye, barley), 4 months
• Soybeans, 15 days
• Dry beans & peas, 10 months

Zest label rotation restrictions—soil pH dependent:

• Sunflower: pH 7.5 or less, 11 months; pH > 7.5, 18 months.

Consult the full label for additional information and special circumstances.  Additional rotational restriction comments include certain states (including Texas), rate of Zest, and if unirrigated drought conditions prevail.

Igrowth (Advanta/Alta)

This ALS herbicide program is paired with the imazamox herbicide Imiflex from UPL.  The technology is the most advanced commercially.  It is available in Australia and Argentina since 2018.  It is available in at least five medium-early and medium maturity hybrids and also one forage sorghum.  Imiflex has both preemergence and postemergence activity that extends to many broadleaf and select grass weeds.  The residual activity from Imiflex appears to be longer than Inzen or Double Team.  What is Imiflex most similar to?—Raptor in soybeans.  Pollen-mediated gene flow to nearby Johnsongrass and shattercane can increase development of resistance in those weeds.  Control of these nearby weeds is recommended when they are also flowering.  See the full Imiflex label for specific instructions on crabgrass control.  Applications recommended for broadleaves ≤3” tall, and grasses no more than 4-5 leaf stage.  Do not apply on grain sorghum >20” tall.  Imiflex has no preharvest interval for any igrowth sorghum crop.

Selected Imiflex label rotation restrictions for Texas may depend on east or west location from U.S. Highway 83 (Canadian-Childress-Abilene-Junction-Uvalde).

• Sorghums (all types, including igrowth), 18 months
• Corn (non-Clearfield), 8.5 months
• Clearfield crops including corn winter canoa, sunflower, wheat, anytime
• Cotton, 9 months
• Non-Clearfield wheat, 3 months; rye, 4 months; oats and barley, 9 months
• Soybeans, most beans & peas, anytime
• Sunflower, 9 months.

Additional rotational restriction comments for soil pH, rainfall + irrigation, and tillage are listed for barley and non-Clearfield wheat.

For additional comments on igrowth/Imiflex see United Sorghum Checkoff agronomist Dr. Brent Bean’s comments, https://www.sorghumcheckoff.com/agronomy-insights/igrowth-imiflex-use-in-sorghum/

Double Team (S&W Seed/Sorghum Partners)

This ACCase herbicide program is paired with the quizalofop herbicide FirstAct from ADAMA.  Currently less information is available on use and timing of FirstAct.  Grass resistance to ACCase herbicides is relatively low compared to ALS herbicides.  . FirstAct is a postemergence, which only has activity on grass weeds. What is FirstAct most similar to?—Assure II in wheat.  Pollen-mediated gene flow to nearby Johnsongrass and shattercane can increase development of resistance in those weeds.  Consult the label for last recommended application to weeds of specific size (most at 2 to 6” tall maximum).  Apply to young, actively growing weeds in 4-20” sorghum for best weed control and crop tolerance.

Selected FirstAct label rotation restrictions:

• Double Team sorghums, do not plant in the same field the following year
• Do not rotate to crops other than cotton, dry beans, peas, canola, sesame, soybeans, sunflower, quizalofop tolerant field corn for 120 days. (This implies there is no rotation restriction to these listed crops, but confirm with a chemical dealer.)

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For all three herbicide-tolerant systems consult the chemical label for additional information on tank-mix partners, possible additives, and the all-important information for rates and number of allowed applications.

What is the cost of these three herbicide programs—both seed and herbicide?

Texas A&M AgriLife has not yet gathered information from companies and dealers on what projected costs may be.  Anticipate they will be somewhat higher as the companies recapture the tremendous cost of bringing these technologies to market.  For Texas Grain sorghum growers that have a regular fight on their hands with grasses, this is where the technology is most valuable.  These technologies will not increase your yield potential but can have a major impact on the actual yield you can obtain if you can greatly reduce the competition of problem grasses.

Are any of these herbicide-tolerant grain sorghum hybrids also tolerant to sugarcane aphid?

At this time, probably not.  Alta notes one hybrid that has some limited SCA tolerance, but it is not one of Alta’s “Aphix” designated hybrids that are marketed for the purpose of SCA control.

Remember Common Rules for Effective Long-term Herbicide Use

• These technologies are NOT a replacement for an effective PRE-emerge weed control program. In spite of these new technologies and numerous existing in-season broadleaf herbicides, for both grasses and broadleaves, your PRE-emerge weed control decisions remain the most important decision you can make for weed control in grain sorghum.  These decisions are about preventive weed control.  For many growers a combination of Group 15 products (s-metolachlor, acetochlor, or dimethenamid-P) and atrazine are good choices for reducing in-season weed pressure.  Let these three new technologies assist you in cleaning up escapes and specifically knocking back grasses that otherwise could swallow your sorghum crop.  Poor grass control can reduce sorghum yields by half or more.  In addition to Johnsongrass and shattercane, these technologies should have effectiveness on Texas panicum, barnyardgrass, foxtails, etc.

• Good stewardship includes that these chemistries are still rotated with other herbicides to reduce the potential for (further) resistance development.

• In the first year that you implement any of these three herbicide technologies, do not assume that you now can simply farm sorghum wherever your grassy weeds are heavy. Though you may want to plant grass-infested acres to a new herbicide tolerant sorghum (and in lieu of a favorite high-yielding sorghum) expect a learning curve on how to best use these technologies.  If you still have a major grass issue with problem grasses then share that issue with your seed dealer, chemical company rep, and/or Texas A&M AgriLife weed scientists.  This may help you identify an area where you may improve your results in a subsequent year.

For information on grain sorghum or sorghum family forages for your area, or for specific questions you have on any topic in sorghum, contact your local county agricultural Extension agent, an Extension crop specialist, or sorghum Extension specialists Dr. Ronnie Schnell, College Station, (979) 845-2935, Ronnie.Schnell@ag.tamu.edu, or Dr. Calvin Trostle, Lubbock, (806) 746-6101, ctrostle@ag.tamu.edu  Your question will be relayed to the appropriate Texas A&M AgriLife staff as needed.