Proper adjuvant use boosts herbicide effectiveness

Tight supplies, inflation, and tough weeds nearly guarantee higher 2023 herbicide costs. One way to boost herbicide performance, though, is through properly mixed adjuvants.
Numerous products fall under the adjuvant banner, but most can be grouped into surfactants, crop oil concentrates, and ammonia fertilizers that accompany herbicides into a spray tank. Adjuvants also include drift reduction agents (DRAs) that curb herbicide off-target movement and pH modifiers that reduce tank mix acidity.  
Adjuvants work by enabling herbicides to get into, onto, and through a weed. ″We must gain every advantage we can to control the target weeds. That’s where the optimization with adjuvants is critical,″ says Bryan Young, a Purdue University weed scientist.
That’s because herbicide costs are climbing. ″A typical Indiana corn herbicide program cost $35 to $45 per acre in 2022, not including application costs,″ Young says. ″Cost for a soybean herbicide program was $40 to $50 per acre. Some soybean farmers were spending $50 per acre just on postemergence weed control. That’s with no preemerge or soil residual program of Enlist One, Roundup, and Liberty.″
In comparison, quality adjuvants can cost $3 to $6 per acre. ″Return on investment for adjuvants can be one to four times the cost,″ he says.
However, adjuvant management is key. If coverage rates lag because of poor adjuvant management, Young says a ″rescue″ post application will cost at least $20 per acre.
Public and company crop protectant consultants can help growers select the right adjuvant for the job. ″They look at how adjuvants vary by product, herbicide site-of-action, weed species and usually have lots of research to test and validate their recommendations,″ says Gail Stratman, FMC regional technical service manager.
Having the right adjuvant in the tank ″will ensure every droplet sprayed is as effective as possible,″ says Connor Ferguson, Wilbur-Ellis branded technologies data manager. ″With contact herbicides, adjuvants help droplets adhere to the leaf surface, increasing contact area for better absorption and efficacy. With systemic herbicides, which move within the plant, it’s important to have the right adjuvant to get spray onto the plant leaves so the herbicide can work effectively. This can be difficult with a heavy weed infestation, waxy-type leaf surfaces, or when targeting an otherwise difficult weed like common lambsquarter. In these cases, oil-based adjuvants can help droplets penetrate tough plant surfaces.″
Herbicide advisers do a good job of identifying and approving adjuvants that can help mitigate off-target movement, including synthetic auxin herbicides that include dicamba and 2,4-D, says James Reiss, Precision Laboratories senior vice president of product development.
″But the real opportunity to maximize overall performance comes from understanding the adjuvant needs of the herbicide tank mix partner that is being added to that auxin application,″ he adds.
High surfactant methylated seed oils (HSMSO) or even high surfactant oil concentrates (HSOC) can drive the performance of the tank mix partner and even improve the auxin herbicide’s performance, he says.