We have received numerous questions this spring regarding the use of herbicide spray additives intended to modify the characteristics of the carrier. The supposed advantage of these carriers is that they reduce degradation of the herbicide within the spray tank, therefore improving performance and possibly allowing a reduction in herbicide rates. At least two types of products are being promoted: additives that reduce the pH of water, and oils that are used to encapsulate herbicides prior to mixing with water.
Many water sources in Iowa are alkaline (pH > 7), but the range of alkalinity found does not affect herbicide degradation, compatibility, or performance. Spending money to neutralize or acidify water is a poor investment.
Encapsulation of herbicides in vegetable oils is promoted as a method of protecting herbicides from factors that interfere with performance. Considerable research has shown no benefit, other than for the traditional uses with postemergence herbicides, to the use of oils as herbicides carriers, encapsulators, etc.
In summary, spray additives serve several important functions in herbicide applications, including increasing postemergence herbicide efficacy (surfactants, crop oil concentrates, fertilizers) and improving handling and application (compatibility agents, defoamers, driftretardants). Additive selection should be based on recommendations found on specific herbicide labels.