Iowa State University
by Bob Hartzler
April 06, 2005 - I'd like to think this ad is an April Fool's Day joke, but unfortunately I believe its the real thing. The ad appears in the March 26 issue of Iowa Farmer Today and promotes two spray additives from Agriliance, Alliance and Class Act. The following statements earn this piece a spot in the Hall of Shame:
"These adjuvants coat the plant and drive herbicide inside, so your glyphosate starts working in just three to five days - killing weeds twice as fast, even during hot, dry weather. "
Herbicide adsorption into plants is a passive process driven by concentration gradients. Spray additives modify the characteristics of the spray solution or plant surface in ways that enhance herbicide movement into the plant, but diffusion is still the process that moves the herbicide. Thus, to say that an adjuvant drives the herbicide into the plant is quite a stretch.
I would have been willing to overlook the above statement, but the claim to increase the speed of kill goes too far. The ad states these adjuvants allow glyphosate to start working in three to five days. Research has shown that approximately 70% of the glyphosate is absorbed by a plant in the first 24 hrs after application (Feng et al. 2000) and that the shikimate acid pathway is disrupted in this time period (Singh and Shaner, 1998). The value of additives with glyphosate is well documented, particularly when using glyphosate formulations recommending additional surfactant or when hard water is used as a carrier. Under these conditions appropriate additives increase the percentage of glyphosate absorbed, therefore enhancing performance of the product. The focus should be on how well a treatment controls weeds, rather than minor changes in how quickly symptoms appear.
Unlike pesticides, spray additives are not regulated, leading to the introduction of inferior products or the use of misleading claims when promoting products. It also is difficult to determine the specific ingredients used in individual products. Alliance and Class Act contain components that reduce the antagonistic effect of hard water, thus they serve as replacements for AMS commonly added to the tank when hard water is used as a carrier. Class Act also contains a surfactant, thus fitting the need for glyphosate formulations recommending addition of surfactants. Both products contain other ingredients shown to enhance glyphosate under specific conditions.
Agriliance is a leader in the development of spray adjuvants and thoroughly evaluates their products prior to introduction. Thus, I do not question the quality or utility of these two additives. However, I do feel the statements included in this ad may contribute to the confusion that complicates the selection and use of spray additives.
Feng, P.C.C., J.J. Sandbrink and R.D. Sammons. 2000. Retention, uptake, and translocation of glyphosate from track-spray applications and correlation to rainfastness in velvetleaf. Weed Sci. 14:127-132.
Singh, B.K. and D.L. Shaner. 1998. Rapid determination of glyphosate injury to plants and identification of glyphosate resistant plants. Weed Technol. 12:527-530.
Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University
more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
or comments here.
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