Overcoming weeds

Specialist Offers Advice To Subdue Weeds In Cotton And Soybeans

JACKSON, TENN.
   Palmer pigweed, giant ragweed and corn as well showed up as weeds in some Tennessee fields last year, according to Dr. Larry Steckel, UT extension weed specialist at the research station at Jackson. The weeds showed up in cotton and soybeans.
   “In these fields they were putting multiple applications of Roundup on the weeds and it was not controlling them, so we are looking at some other options,” Steckel said.
   In a couple of farmers’ fields six-inch giant ragweed appeared, and treatment focused on six-tenths of an ounce of First Rate and 44 ounces of Roundup. That was a $35 treatment but it finally knocked them back. The giant ragweed was confirmed as glyphosate resistant some time ago.
   The ragweed was fairly widespread in counties up and down the Mississippi river on bottom lands. However, it is beginning to move even further inland. While it is more of an issue along the river it is starting to reach the uplands as well.
   “Farmers are getting more and more away from tillage, but now they made a shift back to tillage to take the palmer pigweed and glyphosate resistant horseweed out,” he said. “Again we had a very dry spring last year and we had some inconsistent results with the primary herbicide which is dicamba. We had some soybean farmers trying to offset that by upping the dicamba rate, which was fine for taking out the weeds, but we had dry conditions and in some cases treatment carried over and hurt the soybeans as they came up. If you up the rate over eight ounces you really need to apply it 30 days before you plant and if you get inside that 30 days and it stays dry it will bang up the soybeans when they come up.”
   The moisture is needed to activate the treatment.
   Because of the weed problems, some farmers have been looking at fall applied herbicides.
   “I think in some places that has a fit, but for most of our acres here in Tennessee because we have such rolling ground I am just not a big fan of fall applied,” he stated. “I think it keeps us too clean and our soils are just so highly erodible.”
   Steckel really prefers to spray fields in late January or February when they are smaller and easier to control. Then the ground is typically wetter and better activity occurs with dicamba. Some folks last year heeded that message in cotton and had pretty good horseweed control in cotton.
   The soybean folks waited until just before they were going to plant and these people had problems in the field. Steckel feels the February/ March treatment is also a good option for soybeans.
   “I think a lot of farmers are not as concerned about burning down horseweed in soybeans as they are in cotton because in soybeans we do have an option,” he said. “It is called First Rate, but the thing with First Rate is they are waiting until it gets too big before they even spray it with that.”
   The wait makes it too late, he said. Another thing that concerns him is that First Rate is an ALS herbicide and there are ALS resistant biotypes of horseweed in other states. In Indiana they have confirmed that it is Glyphosate and ALS resistant.
   “I am afraid it is just a matter of time before we have it here, then we have no options in soybeans so I would like to keep that in my pocket as long as possible and not have to rely on it every time,” he summed. Δ

Dr. Larry Steckel, UT extension weed specialist explains farmers are getting more and more away from tillage, but now they made a shift back to tillage to take the palmer pigweed and glyphosate resistant horseweed out. Photo by John LaRose