On September 12, 2024 the Wisconsin Extension Weed Management Team held a workshop at the University of Wisconsin-Madison Arlington Agricultural 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 by about 90 participants from across Southern Wisconsin and Northern Illinois. Watch a short recap of the day here.
The keynote speaker was Dr. Tommy Butts, Clinical Assistant Professor, Extension Weed Scientist 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.
Navigating New Technologies for Drift and Weed Control
Our first presenter, Dr. Tommy Butts, covered application technology related to drift and weed control. Butts dug into the effects of spray volume, spray pressure, droplet size, and nozzle selection on herbicide effectiveness. Participants found nozzle size and consequently droplet size to be the most valuable and applicable information. While surfactants help with droplet size and coverage, we learned that nozzle type makes a much larger difference. Changing from an XR 110025 @ 60psi to a TTI11005 @ 30psi, for instance, reduced the percentage of drift-prone fines from 25.8% to 2.8% according to data presented by Butts.
Droplet size should be tailored for the specific application need; for example, larger droplets are better for canopy penetration and for pushing fungicide to the ear leaf while small droplets will keep the product near the top of the canopy. Butts has also conducted recent research comparing coverage from a drone application versus a ground rig. The results of this research showed similar spray coverage and weed control efficacy when spraying Gramoxone with either a 5 gal/acre drone application or a 10 gal/acre ground rig application; however, droplet distribution was not even across the spray swath of the drone with any combination of nozzle or carrier volume resulting in a non-uniform pattern. Watch Dr. Tommy Butts’ presentation here.
Herbicide & Weed Management in Alfalfa
Dr. Mark Renz joined us to help weigh decisions related to herbicide programs and application timing in alfalfa. We learned that weed control prior to the first cut in the seeding year can increase quality but may decrease total yield due to reduced weed biomass. Predominant weed species may influence this decision based on their feed value and palatability. The most common grass herbicides are Poast and Select. When thinking about broadleaf control, farmers need to consider herbicide-resistant weeds present in their fields. Roundup-Ready alfalfa, while convenient for some weeds, is of little use against resistant waterhemp, growers should instead consider a residual herbicide, such as Warrant in combination with Roundup in a post application just after alfalfa emergence.
Raptor is another POST-emergence option to control certain broadleaf and grass weeds; however, it must be applied after alfalfa reaches the 2nd trifoliate stage and before weeds exceed three inches, which makes timing critical and sometimes impossible. Renz discussed that herbicide applications after the first cut in the seeding year are usually not needed if farmers have more than 4-5 plants or more than 55 stems per square foot. If the alfalfa density is lower than this, weed management is not guaranteed to increase alfalfa yield; however it may increase quality depending on weed species and pressure. Find more information on the Renz Weed Science page here.
WiscWeeds Presentation
Dr. Rodrigo Werle and the WiscWeeds Team (Zaim Ugljic, Daniel Zhu, and Dr. Ahmad Mobli) highlighted a handful of current research projects and recent recommendations. They started by highlighting the importance of even spray coverage when using novel targeted herbicide application technologies such as See & Spray with the results from an experiment showing multiple nozzle activation upon weed detection translating to significantly better spray coverage and weed control when compared to single nozzle activation.
Next, they discussed research comparing Enlist One and Liberty alone with a tank mix of both. Tank mixing with both products provided better and more consistent waterhemp control. They also covered another herbicide synergistic effect, the popular atrazine + mesotrione combo for POST-emergence weed control in corn. However, with increasing restrictions on atrazine and the relatively short window for application (up to 12” tall corn) other photo-system II inhibitor herbicides may be a better option, but do they provide the same synergism with mesotrione as atrazine? Yes, results from this year’s plots showed bromoxynil combined with mesotrione provided better waterhemp and giant ragweed control than either product alone.
Dr. Werle highlighted some results from the continued effort to suppress weeds with a cereal rye cover crop in soybeans. He reminded growers that around 4,500 pounds of rye biomass or a thick stand of around 30-inch-tall plants is needed to adequately suppress most waterhemp and giant ragweed plants. Results from their systems trial established 6 years ago showed high cereal rye cover crop biomass not only provides weed suppression but also higher soil aggregate stability and percent total carbon.
Dan Smith finished up the WiscWeeds presentations with a timely bit on combine cleaning. We learned that for several weed species, especially some of the worst ones such as waterhemp or Palmer amaranth, a great majority of weed seeds stay on the mother plant until harvest. This is why combines are such great distributors of weed seeds. The top three locations for weed seeds to hide in combines are the rock trap, header, and feeder house. Smith mentioned he has done 19 combine cleaning clinics and 17 of those combines had weed seeds on them. The other two machines were brand new! More on combine cleaning here and more from the WiscWeeds team here: www.WiscWeeds.info or https://twitter.com/WiscWeeds
Understanding The Chemistry Behind Herbicide Applications
After lunch, Dr. Tommy Butts graced us with a second presentation 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 accurately. When conditioning spray tank water, it is essential to add the water conditioning agent first before any other products.
Compatibility jar 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 herbicide antagonism can cause poor grass control when tank mixing grass herbicides like clethodim with auxin herbicides like 2,4-D or dicamba; consider spraying these modes of action separately. Butts second presentation can also be viewed on our YouTube Channel here.
Outdoor Demonstrations
The day concluded with demonstrations from sponsors and other partners. First, our TeeJet colleagues Dr. Debora Latorre and Kevin Humke explained their different nozzle types and showed the spray patterns using laser interception. Then the group headed outside to hear Dr. Erin Silva, Dr. Brian Luck, and Ben Brockmueller of UW-Madison discuss organic weed management and look at some of the equipment used such as roller crimpers, tine harrows, and an inter-row mower. Next was a demonstration of the new precision application technology from One Smart Spray by Aaron Hunsinger, which uses artificial intelligence-powered cameras on the spray bar to directly target the weeds. This demonstration received a lot of interest as the technology was able to identify and spray a distinct area around an identified target; check out the video here. Finally, Jeremy Williams with American Drone discussed the advances being made in drone application technology and discussed the pros and cons of various drone equipment options.
Participant Response
Overall, participants were pleased with the event, as 100% of survey respondents indicated that they plan to use the information in their weed management decisions next growing season and beyond. Attendees noted that the importance of scouting fields to support weed management decisions, a perennial topic, was an important takeaway, and that the blend of industry and academic topics was valuable.
Watch The Recap
Thank You
We would like to express our sincere gratitude to the sponsors, presenters, and research station staff for their invaluable contributions to the success of this workshop. Your support and expertise have been instrumental in creating a stimulating and informative event. The UW-Madison Extension Weeds Team is already planning to hold this event next year, so be on the lookout for details to attend!