Adjuvants play a key role in herbicide formulations and spray mixtures to help herbicide performance either by improving herbicide activity or increasing ease of application. Adjuvants are also specific for each product as researched and developed by the herbicide manufacturers. That’s why it’s so crucial to remember that herbicide labels are the most important source of information for adjuvant recommendations that cover diverse use situations and tank mixtures.
Since herbicide spray adjuvants impact how much herbicide enters the plant, they can impact weed control and crop safety. That is why it’s important to follow the label requirements for each herbicide. Each herbicide product has unique adjuvant requirements that are specified on the product label. The label will provide guidance and adjuvant options to address tank mixtures, environmental conditions or weed species characteristics. Some herbicide products, including Roundup PowerMAX® 3 Herbicide, are formulated with sufficient adjuvants in the herbicide formulation and may not need additional adjuvants added to the spray mixture. However, some products have specific recommendations for spray adjuvants that the applicator must add to the spray mixture. Applicators should always pay particular attention to label instructions for each tank-mix product because label recommendations for adjuvants may differ for each product. There is a diverse array of adjuvant products and brands. Different herbicide manufacturers may have supplemental labels or fact sheets that provide additional guidance for the use of adjuvants for specific weed species, crops, tank mixtures or application situations. Applicators must understand the composition and function of each product — while considering expected environmental conditions at the time of herbicide application — to properly match the adjuvant to individual herbicides or tank mixtures. Comprehensive information on commercially available adjuvants can be found at http://siu-weeds.com/adjuvants/index-adj.html.
Varieties of adjuvants that are used with herbicides include nonionic surfactants, oil concentrates, ammonium N fertilizers, spreader-stickers, wetting agents and penetrants.1,2,3,4 Here are some of the most common adjuvants used today:
Table 1. Adjuvant recommendations for Bayer herbicides.
Assumptions unless otherwise stated: AMS and UAN are spray-grade quality, NIS at 80% concentration, MSO at least 80% MSO and 10% emulsifier.For additional information, contact your local Bayer representative.
1Jordan, T, Johnson, B., and Nice, G. 2011. Adjuvants used with herbicides: Factors to consider. Purdue University. https://extension.entm.purdue.edu/pestcrop/2011/issue25/index.html#adjuvant.
2Curran, W.S. and Lingenfelter, D.D. 2009. Adjuvants for enhancing herbicide performance. Agronomy Facts 37. Penn State Extension. https://extension.psu.edu/.
3Hartzler, R. 2013. (Re) learning to accept herbicide injury to crops. Iowa State University, https://www.extension.iastate.edu/.
4Hartzler, B. 2001. Role of spray adjuvants with postemergence herbicides. Iowa State University Weed Science Online https://crops.extension.iastate.edu/encyclopedia/role-spray-adjuvants-postemergence-herbicides.
Web sources verified 6/29/21. 1034_S3