Adjuvants alone won’t solve glyphosate resistance

Adjuvants are very useful products which are used to enhance the activity of postemergence herbicides. Numerous adjuvant products from very reliable distributors are marketed annually and provide a true value to growers seeking to optimize herbicide performance. However, since the adjuvant industry is not regulated as stringently as the pesticide industry, we occasionally run into products that create a lot of attention because of extravagant claims made by the manufacturer or distributor.
 

Nanotechnology is a new and exciting area of research and product development in numerous sectors. Agrochemicals, including adjuvants, are being developed with nanotechnology and may very well have substantial benefits. However, during our winter grower meeting season, we began to hear rumblings about certain “nano” adjuvants and how they provided the answers for control of herbicide-resistant weeds.  Our concern grew after reviewing the marketing material that inaccurately describes the underlying mechanisms of herbicide resistance and the suggestion that the only necessary action to control glyphosate-resistant weeds was to apply glyphosate with the nano adjuvant. The nano adjuvants purportedly would overcome resistance mechanisms and by promoting higher levels of herbicide penetration into the plant. No scientific evidence exists that would suggest weed resistance to glyphosate is simply a lack of foliar absorption. Nonetheless, we were getting phone calls about their utility and were hearing claims that there was university data to support their claims. However, we at Purdue University had not worked with these compounds, nor were we aware of university data supporting their use.
 

Below is a copy of the “technical” data information provided by the distributors for two nano adjuvants, one of these was being marketed in Northern Indiana.  A number of interesting claims are made on these documents, which you can read, by clicking here and here.
 

In an effort to learn more about the utility of these adjuvants, we conducted a study at a site in Indiana with glyphosate-resistant Palmer amaranth and wanted to share the results in this article. Dr. Young has also collaborated with a number of other weed scientists throughout the Midwest to conduct similar trials and we will share the results as they come available.
 

Our trial was on glyphosate-resistant Palmer amaranth with a population of about 95% resistant:5% susceptible.  Control with glyphosate alone was 13.8%. There was a 5% increase in activity with one of these adjuvants at 27 DAT compared to glyphosate alone, but that only raised the level of control to 18% which is still well below commercially acceptable levels.  In other words, the nano adjuvants tested did not solve weed resistance to glyphosate.
 

Adjuvants are critical components of making effective herbicide applications to control our most problematic weeds.  However, the simple addition of an adjuvant to resolve weed resistance to herbicides does not exist.  Be critical of any marketing claims that sound too good to be true, because most of the time they are.