Scouting And Stewardship

Agronomist Offers Tips For Controlling Resistant Weeds

SIKESTON, MO.
   Glyphosate resistant weeds, specifically Palmer pigweed and common waterhemp, and ways to control them was a topic discussed recently by Dr. Anthony Ohmes, Mississippi County Regional Agronomist.
   “These two pigweed species are our predominant pigweed species here in southeast Missouri, as well as across the river in Tennessee and across our state line into Arkansas,” he said. “It’s become one of our super weeds that we and our growers are dealing with each year; and with the rise of glyphosate resistance we’re relying on products that are in the PPO family of herbicides and products such as glufosinate (Ignite or Liberty) in LibertyLink soybean as well.”
   The list of available postemergent products is relatively short. Therefore, stewardship of those products is super important.
   “We must utilize them as tools, in particular with Palmer pigweed and waterhemp we must operate on the concept of zero tolerance,” Ohmes added. “We must eliminate the pigweed out of the field to reduce the seed bank, because one of the weaknesses of Palmer and waterhemp is they have a very short seed life, typically five to six years maximum. If we can eliminate the seed production in the field then that will help eliminate or reduce the population that will take yield from our growers.”
   Another area of discussion was the utilization of herbicides with different modes of action. Rotation of crops and rotation of chemistry helps for a two-fold reason.
   “One, we don’t want to develop resistance in the short list of products that we do have available to us, and two, it also helps with that cultural practice of reducing that seed population,” he said.
   Ohmes also talked about timing. Herbicide timing is essential, especially with post emerge products. These products need to be applied early. So farmers need to be scouting early, getting out in the field and looking for those one- to two-inch tall pigweeds to make that application call for the PPO and Ignite products. Both of those are contact herbicides and must be applied while weeds are small.
   He also talked about overlapping residuals, utilizing preemerge as either a burn down with a residual, or a true pre behind the planter.
   “We want to utilize residuals. Then if we are coming back with a post we need to utilize another residual, be it the residual component in the PPO, post emergent product or a LibertyLink system, utilizing a residual tank mix with the Ignite,” he recommended.
   “We want the concept of zero tolerance, overlapping residuals, scouting early, getting out in the fields and applying our products post emerge products as soon as possible, not waiting for everything to come up,” he urged. “Even though a product like Ignite is a broad spectrum herbicide, we don’t want to get back into the habit of waiting.”
   While farmers are intent on suppressing the proliferance of weeds, they must also be mindful of their neighbors and the potential for drift.
   “We know things can happen,” Ohmes said. “With a contact chemistry, we need to understand our products and understand the typical injury symptoms to various crop plants. A good plan is to use best management practices to both avoid resistance and herbicide drift.”
   He urged farmers to have a backup plan because the unexpected can happen.
   “With Palmer being a very aggressive and fast growing weed, there’s a limited number of days, typically one to three, for applications. So utilize other resources. If you know you can’t get across all your beans in that amount of time, then you need to have some other plan. Things happen and we need to plan ahead, get things lined up for the season.
   In his take home message, he emphasized scouting.
   “Our growers need to utilize scouting and identifying weeds properly. Since we’re dealing with contact herbicides that specifically target certain weeds, we need to know what those weeds are,” he said.
   “In addition to scouting, we also need to be good stewards of our products because there are a limited number of them available, particularly for our Palmer pigweed and waterhemp,” Ohmes stressed. “We need to be good stewards of those products, make sure we’re rotating them, rotating our crops and just preserving the limited resources we do have in our weed control fight.” Δ
   BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower

Dr. Anthony Ohmes, Agronomist with the University of Missouri extension, discussed glyphosate resistant weeds and their control. Photo by John LaRose, Jr.