On September 12, 2024, the Wisconsin Extension Weed Management Team held a workshop at the Arlington Research Station. This was a full day workshop featuring multiple speakers, hands-on demonstrations, a weed knowledge contest, and sponsor exhibits. The event was well attended with 89 participants from across Southern Wisconsin and Northern Illinois. The keynote speaker was Dr. Tommy Butts, Assistant Professor of Weed Management at Purdue University. Other speakers included Dr. Rodrigo Werle and the WiscWeeds Team and Dr. Mark Renz from the Plant and Agroecosystem Sciences Department at UW-Madison, and Dan Smith from UW-Madison Division of Extension Nutrient and Pest Management Program.  

Understanding the Chemistry Behind Herbicide Applications

Dr. Tommy Butts also presented on the chemistry of herbicide applications. Spray water quality was a popular topic with a handful of good questions; the decision to add AMS to the tank when mixing for water conditioning was a common take-home point for participants. Butts also explained that water hardness and pH are not inherently linked like many folks assume and it’s important to get your water tested so you can correct either condition correctly. When conditioning spray tank water it is essential to add the water conditioning agent first before any other products.

Compatibility tests are also a necessary step in an effective tank mix. Butts talked about the potential for herbicides to separate or precipitate but also explained how some products, especially micronutrients, may increase the fines and subsequently the drift potential of the mix. Butts had a handful of herbicide tips for us at the end of his presentation. Consider the way you load the sprayer, flush the induction tank after every product, and never add more than one concentrated product to the induction tank at once. He also noted that herbicide antagonism causes poor grass control when tank mixing grass herbicides like clethodim with auxin herbicides like 2-4D or dicamba; consider spraying these modes of action separately. Watch below.