SUPPORTED BY ENDORSED BY 62 / SEEDWORLD.COM FEBRUARY 2018 For most effective control, Palmer amaranth seedlings should be treated before they are more than four inches tall. PHOTO: UNIVERSITY OF NEBRASKA-LINCOLN aboveground weeds, but also include the residual herbicides to maintain that control. The growers who use lay- ered herbicides for both pre- and post-residual control have a good weed control program. Group 15 chemistries, for exam- ple, provide several weeks of residual control, he says. Use alternate group numbers, Waldstein also advises. “It is important to understand that two different products might have the same site of action, so there would be no value in mixing the two.” Using different sites (or modes) of action is key. This can be accomplished with tank mixes, premixes or alter- nate applications, Waldstein notes. Zidua Pro herbicide is an example of a new soybean pre-emergence herbicide with built in resistance man- agement from three sites of action (Groups 2, 14 and 15). With a product like Zidua PRO, a user does not have to put together an individual chemistry cocktail, but can target multiple sites of action with one premixed product. Finally, Waldstein advises not to let weeds produce seeds by escaping. “This seems straightforward, but it is not uncommon to see a field with a few large weeds in August. We used to think that getting 90 percent control was not bad. But now, with some of these difficult to con- trol weeds, if we only get 90 percent control, many weeds are escaping and creating problems for the future.” However, Young reminds growers not to forget the other side of the equation. “We also have to focus on management strategies that are non-herbicide based. To say you’ll manage resistance long-term with just herbicides is counterintuitive. It’s not sus- tainable,” Young says. “We have to think about things like row spacing and seeding rates. Tillage can also be of use, when it can be done appropriately and depending on the production system. Proper crop rotations are also key.” Waiting Game Another reason to incor- porate practices that don’t rely on herbicides is the fact that there aren’t currently enough new sites/modes of action coming to market like there were at one time, Young notes. Growers should develop good management practices along with respon- sible use of herbicides for this very reason. “We’re in a major product development drought — the last mode of action brought to market was discovered in the 1980s,” Young says. “The advent and rapid adoption of glyphosate-resistant crops reduced the need for new herbicide discovery, so we essentially have taken a bit of a vacation from herbicide discovery, in many respects.” Waldstein echoes that sentiment. “It’s always a major investment to develop a truly new site of action. However, BASF’s philosophy is to develop and release new products with multiple chemistries and multiple sites of action,” he says. “I would like to tell all our customers that we will have five or 10 new sites of action coming out in the next few years, but in reality, that’s not the case. This means it’s even more important to steward the effective tools we cur- rently have in our toolbox.” The key to combating weed resistance isn’t just responsible use of herbicides and adoption of non-herbi- cide management practices. Education is also key, both experts agree. “Education is absolutely necessary; a large portion of my time is spent helping users understand how to effectively use different chemistries,” Waldstein says. Young concurs. “When we’re adopting new technologies, like dicamba- tolerant crops, we need to be good stewards, which includes making sure we manage against any resist- ance to dicamba but keeping the herbicide on target.” SW