Key Takeaways
Know your sorghum trait: Confirm which herbicide-tolerant sorghum technology, if any, a hybrid carries before choosing a postemergence herbicide.
Read the label: Follow the most restrictive growth stage, height or tank-mix requirement for every product going into the sprayer.
Time it right: Apply trait herbicides inside their labeled window early enough to catch small weeds, but not before the crop has reached the minimum stage required for crop safety.
Avoid stress: Herbicide injury risk climbs when the crop or weeds are under drought, heat or cold stress; both should be actively growing at application.
Protect the technology: Scout for and control shattercane and johnsongrass escapes, particularly around flowering, to slow the development and spread of herbicide resistance in sorghum's weedy relatives.
Sorghum is an important option in dryland and limited-irrigation systems across the Great Plains. But because the crop is highly sensitive to weed competition, particularly during the first five weeks after planting, timely weed management is critical.
Weed management is challenging in sorghum, particularly for grass weeds, because fewer herbicides are labeled for use in sorghum than in corn and soybean. As the residual activity of preemergence herbicides declines, timely postemergence applications become important (Figure 1). Each postemergence herbicide has label restrictions based on sorghum growth stage, plant height or both (Table 1).
| Postemergence Sorghum Herbicide | Sorghum Growth Stage or Plant Height |
|---|---|
| 2,4-D Amine (4L) or 2,4-D Ester (4L) | 5 inches; early boot stage |
| Aim EC | Less than 12 inches; 3-5 leaf |
| Atrazine DF | 12 inches |
| Buctril | 3 inches to 12 inches |
| Dicamba | 3-5 leaf |
| Diquat | 7-14 days prior to harvest |
| FirstAct (Only for Double Team Sorghum) | Emergence; 45 days before-harvest |
| Huskie | 3-leaf to 30 inches; prior to flag leaf |
| Huskie FX | 3-leaf to 30 inches; prior to flag leaf |
| Imiflex (Only for iGrowth sorghum) | Can apply up to 20 inches iGrowth sorghum; Never replant iGrowth sorghum in consecutive years |
| Paramount | Emergence; 12 inches |
| Peak | 5 inches-30 inches |
| Permit | 2-leaf; before head emergence |
| Starane Ultra | 3-7 leaf; 8-leaf to boot use drop tips |
| Yukon | Spike to 36 inches |
| Zest (Only for Inzen sorghum) | Emergence to 20 inches |
Herbicide-Tolerant Sorghum
Double Team™: This trait provides tolerance to quizalofop, a FOP herbicide in the ACCase-inhibitor group used for grass control. The labeled herbicide is FirstAct, which has the active ingredient quizalofop. This technology was developed by S&W Seed Co., and FirstAct is sold by ADAMA.
Inzen™: The Inzen trait provides tolerance to nicosulfuron — a sulfonylurea herbicide family, which is a subclass of the acetolactate synthase (ALS) inhibiting herbicides. The technology was developed by Corteva (Pioneer), and the herbicide labeled for use with Inzen is Zest, which is sold by Corteva.
iGrowth®: This sorghum trait provides tolerance to imazamox, an imidazolinone herbicide that inhibits acetolactate synthase (ALS). The technology was developed by Advanta Seeds, and the herbicide labeled for use with iGrowth is Imiflex, which has the active ingredient imazamox and is sold by UPL.
Stewardship Considerations for Herbicide-Tolerant Sorghum
- FirstAct (quizalofop) should not be tank-mixed with broadleaf herbicides. Label guidance calls for applying herbicide containing dicamba or 2,4-D at least one day before or approximately a week after the FirstAct application to avoid reduced grass control.
- Although both iGrowth and Inzen rely on ALS-inhibiting herbicides, they belong to different chemical subclasses and aren't interchangeable for resistance management. A weed population resistant to one may be cross-resistant to the other, so rotating between the two isn't a dependable resistance-management strategy.
- Don't plant sorghum into fields with known ALS-resistant shattercane or johnsongrass.
- Don't plant grain sorghum of any kind the year immediately following an Inzen sorghum.
- Use preplant burndown herbicide ahead of planting herbicide-tolerant sorghum rather than counting on the trait herbicide to clean up an already-weedy field.
- Spray at the full labeled rate while weeds are small (less than 6 inches), then scout afterward to confirm control was achieved.
How to Determine Sorghum Growth Stage
Sorghum growth stage can be determined by counting leaves with a visible collar, starting with the lowest rounded-tip leaf at the base of the plant. Leaves still emerging from the whorl without a visible collar aren't counted. Because label restrictions are often given by leaf stage and plant height — and, for several products, by reproductive stage such as boot or flag leaf emergence — follow the most restrictive criterion listed on the label. The same principle applies to tank mixes: application timing must meet the most restrictive requirements of all products in the tank.
Boot stage is worth noting specifically because growers accustomed to staging corn by leaf number won't find a directly corresponding stage. In sorghum, boot stage occurs when the developing panicle is still enclosed within the flag leaf sheath, just before head emergence. It marks an application cutoff for several postemergence herbicides. For example, 2,4-D is not labeled once sorghum reaches boot stage, and quinclorac products carry a similar restriction.
For sorghum herbicide efficacy ratings by weed species and current use rates, refer to the Nebraska Extension NebGuide EC130, “Guide for Weed, Disease and Insect Management in Nebraska,” available for purchase online.
Mention of a trade name does not constitute an endorsement of that product by the University of Nebraska-Lincoln, nor is discrimination intended toward similar, unnamed products. Always read and follow current product label directions.
