N E W GROU N D
Stop the weeds, spare the wheat �� U of M grassy weed trials compare efficacy, crop safety to aid grower decisions. Wild oats and other grassy weeds are the most expensive weeds to control for Minnesota growers, says Bev Durgan, extension weed scientist with the University of Minnesota.
results from post-emergence wild oat herbicides following weedy fallow and mechanical cultivation. The injury is measured visually and rated compared to a non-treated check.
“Generally, a grass herbicide costs more, and there are multiple options, so I look at trying to get the most efficacy,” she says, comparing factors including weed control, application timing, tank-mixes with other herbicides and crop tolerance across hard red spring wheat variety releases from Minnesota, North Dakota and South Dakota.
“We also take height, so if there is a reduction in height due to a herbicide, that is also something that a grower will see, especially if he has treated a field and sees a skip in it,” she says. “But reductions in height don’t always mean reduction in yield; there’s not a direct correlation to yield loss.” Yield is recorded in all the plots and also compared to the non-treated check.
“In general, you want to see that 90-plus-percent control of grassy weeds, especially wild oats,” Durgan says. “For foxtail, that’s not quite as important, but for wild oat control it is. Wild oats are more competitive, so you’ll get yield loss. Also you will get seed production.
In the 2012 trials, applications of Everest 2.0 Herbicide at 0.75 oz/acre on average showed only 4.5-percent crop injury vs. 9.8 percent for Huskie® Complete and 11.2 percent for GoldSky®. The crop safety paid off in yield, with Everest 2.0 averaging 56.9 bushels/acre vs. 54.9 and 54.5 for the other two, respectively. Percent of wild oat control was in the high 90s for all products in these plots.
“Wild oat seeds remain in the soil a longer period than foxtail does, and so, keeping that seed bank going with wild oats means that you have to continue to control them. Foxtail is less competitive, and lots of times, with a good wheat stand, you don’t get a lot of seed production with foxtail. But wild oats are taller than the wheat, and they’ll come up and produce seed.”
�� Minimize crop injury Small grain growers have very little tolerance for crop injury, she says, so Durgan and her trial collaborators look closely at which herbicides do the best job of stopping yield-robbing weeds without harming the growing wheat or the bottom line. “They don’t like to see that crop injured,” she says. “So, obviously, I want to make sure I’m giving growers the best information on the best way to control at the most economical rate, and to prevent injury. But if they do get injury, I also want to help them understand what the causes are and whether they are going to see a yield loss, because not all crop injury directly becomes a yield loss.” So one of her goals is to give growers an idea of what is to be expected, what influences crop injury and how a crop can recover. For example, she notes that in general, ACCase (Group 1) wild oat herbicide products “tend to produce less crop response (injury) and often higher control, however, we also have a lot of resistance issues around ACCase herbicides. So there has to be this rotation with another class of herbicides, the ALS herbicides (Group 2), to prevent resistance.”
�� Everest 2.0 trial results In grassy weed trials over the years at Crookston and Rosemont, Minn., Durgan compares crop injury and yield
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“When Everest first came on the market, it had a different formulation, and in my trials, I did see a higher rate of injury,” she says. “Everest 2.0 does give quite a bit of crop safety vs. the older formulation.” Everest 2.0 was introduced in 2011 with advanced safener technology. The safener cloquintocet mexyl is built into the formulation. “What you see in the data is really true. We consistently tend to see less crop response with the Everest 2.0 than we have in the past. And over a number of years, Everest 2.0 does tend to give less injury than Huskie Complete or GoldSky.” In addition, in the 2012 U of M crop tolerance trials, Everest 2.0 consistently showed the highest crop safety across all six hard red spring wheat varieties grown in weed-free plots. On average across all varieties treated in the trials, the percentage of crop injury with Huskie Complete was two times that seen with the Everest 2.0 treatment. Trial results and analysis from Durgan’s research going back to 1997 are available online at http://appliedweeds.cfans.umn.edu/research.html. Durgan emphasizes that while her team is always looking for the most cost-effective control with the least injury, “we also are sure that we look at options to help growers manage resistance. They have to be looking at how to manage these weeds and looking at what they’re using in their herbicide combinations and rotations, so that they are not using them for multiple years without changing classes. Just switching from using one class repeatedly and going to the next class is not going to solve the resistance problem.” ❦