Outwitting Weeds

 Dr. Larry Steckel, University of Tennessee weed scientist, 
 spoke on the topic of atrazine and how long it’s lasting.

 Photo: John LaRose Jr.

Before Late Frost Is Critical Time For Pigweed Seed Spread

MidAmerica Farmer Grower

   Corn weed control, past and future, received the attention of those present at the University of Missouri Field day in Miner, Mo., recently, when Dr. Larry Steckel, University of Tennessee weed scientist, presented the topic.
   Steckel’s first focus was on atrazine and how long it’s lasting. A number of studies have been done where atrazine was used on soils,
   “We found that if it’s used over time we build up microbes in the soil that eat atrazine,” he said. “As a result, it doesn’t last. We actually did a study where I pulled soil out of a corn field in west Tennessee and we sent it off to my colleague, Tom Mueller, weed scientist, who did an atrazine test on it, comparing it to soil he pulled right off the Knoxville campus that had never seen atrazine. Long story short, where atrazine was put on that soil, from the Knoxville campus that had never seen atrazine, it lasted three weeks. We got three weeks residual out of it and that’s what we expect.
   “The soil I pulled out of this corn field in west Tennessee where atrazine was used, the residual on that for atrazine lasted three days,” Steckel reported. “Since then Mueller has expanded the test. He’s tested soils all over Missouri, Arkansas, Illinois, Ohio, Indiana, and it’s the same everywhere. We’re not going to get a lot of residual control out of atrazine. The best way to manage that product is to use it as a post emergence product and get the value out of it that way.”
   Next, Steckel focused on palmer amaranth management in corn, noting that big populations are building up in soybeans and cotton crops and farmers are rotating to corn to try to manage it.
   “We need to do a good job in corn,” he said. “One of the first calls I get particularly on a spring like last year where folks planted but couldn’t get in and spray in time is controlling large Palmer amaranth in big corn. You start getting into label constraints when you do that with certain products and big pigweed is hard to control even with some good corn herbicides.”
   Steckel mentioned several pre mixes as well as some more common premixes in use today like Halex GT, Caprino, or Realm Q.
   “Once corn gets bigger, as much as 12 inches, atrazine is out; that’s the cutoff when we start looking instead to those products which we need to control big pigweed, products like Status or a Dicamba type product. However, most notably Status has a safener in it so you can put it on big corn safely and get good results with that.
   “Finally, after corn harvest weed control is a big, big  key issue,” he cautioned. “We can do a good job with a lot of corn herbicide to managing pigweed in season; but as soon as we harvest our corn in August, September, that’s a critical time, especially this year. Palmer pigweed can sprout and grow for two or three months before frost; it can produce seed and you’re going to have to manage that next year.”
   Steckel reported a project a graduate student worked on where she went out after corn harvest and made some herbicide applications to control the pigweed after harvest.
   ”Long story short, that effort decreased the soil seed bank by 17 million seeds of Palmer per acre, so that can be a big plus in helping us manage pigweed in soybeans or cotton the next year.”
   In another issue, Steckel reported on testing a hooded rig that goes onto the back of a cotton planter and is designed for applying dicamba or 2,4-D preemerge with the new technologies that are coming on the horizon, the Roundup Extend Cotton and the Enlist cotton.
   “With these varieties, we can put dicamba  or 2,4-D on preplant,” he said. “We’ve been looking at these rigs, and really we’ve had good luck with them this first year out using them. They have just one nozzle on them, but we’re getting good coverage on the soil surface with them. They’re constructed in a way that the spray can’t drift. So, when you’re planting you don’t have to consider what the wind is going to do, you can just go out there and plant.”
   A preemergence application of dicamba can be used with the Extend Cotton, or 2,4-D with the Enlist cotton, and with this rig it will stay put. Even on a very windy day, it’s not going to move.
   “That’s a big plus in my mind,” Steckel added. “Say you’re planting Roundup Extend Cotton, preemerge is one of the best times to use dicamba (when it gets labeled) in that system in my opinion. You can use at least a pint; you can even go higher and with that rate you can get some decent residual out of it. You do need to tank mix something else in with it, like a Cotoran or Caparol, some of these traditional pres we’ve been using; but if you do that you’re going to have a lot more consistent pre than we have today. You may or may not use it post in crop, but using it preemerge is a very safe way to use it just getting right out of the gate at planting in the spring.” ∆
   BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower
MidAmerica Farm Publications, Inc
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