The activity of many foliar-applied herbicides depends on the appropriate use of spray additives. The primary purpose of additives is to improve absorption of the herbicide into the foliage of weeds. A notable exception to this is when AMS is used with Roundup. The AMS prevents glyphosate (active ingredient in Roundup) from being inactivated by cations that may be found in the carrier. The best source of information for determining the most appropriate additive is the herbicide label. Manufacturers conduct extensive research each year to determine how to maximize the performance of their products, and the label recommendations reflect their findings.
Selecting an additive can be confusing, because there are literally hundreds of products on the market. Research at ISU has shown little difference among reputable products within the same class of additive (i.e., all non-ionic surfactants are pretty much alike). Be wary of products that claim benefits other than improved herbicide absorption. In recent years, several products have been promoted for their ability to stop herbicide degradation in the spray tank (alkaline hydrolysis, etc.). This is not a problem with the herbicides and water sources used in Iowa. Also keep in mind that using a specific additive does not allow herbicide rates to be reduced.