Dr. Eric Prostko, Weed Scientist with UGA Cooperative Extension, has sent news about possible issues with tank mixes between Roundup (glyphosate) and Atrazine. The following is a post that he forwarded to our offices about the issue.
Over the last few days, I have been bombarded with questions regarding problems with Roundup + Atrazine tank-mixtures. Some folks have observed foaming problems while others have observed sludge/precipitate problems. Most of the complaints I have received have revolved around the use of Roundup PowerMax and Roundup WeatherMax. I am not really sure what is going on since I have not experienced any problems this year with my own tank-mixtures (Roundup WeatherMax + Aatrex). I do know that Atrazine can be a difficult formulation to handle since it goes directly to the bottom of the spray tank when dumped into water. Thus, aggressive agitation with any flowable herbicide formulation is important. After scouring the world for some help with this problem, I came across the following publication from Monsanto which might be of use to your growers: