Conservation tillage, a critical practice in farming for a carbon market, demands a different approach to weed control.
“Weed management in conservation tillage systems puts an increased burden on chemical control,” says Josh McGinty, Texas AgriLife Extension agronomist, Corpus Christi.
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McGinty discussed the challenges farmers face with weed management, especially herbicide resistant weeds, during a “Carbon Farming in Texas” workshop, held in-person and online recently in Robstown.
The finer points
McGinty said no-till production puts “a greater emphasis on the ‘finer points’ of weed control.” Those points include:
Scout and identify problem weed species, including herbicide resistant species.
Overlap residual herbicides from preplant through early- to mid-season.
Apply postemergence herbicides at the right time and to the right size weed.
Manage weeds in field margins and roadsides.
Rotating crops and technology are more important than before.
McGinty also said cover crops may be useful in weed control. “But it’s a balancing act with moisture, providing enough for the cover without robbing the cash crop.”
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A strip-tilled field at the Corpus Christi Texas A&M AgriLife Research Center where Valor is used to keep it clean over the winter. (Photo by Josh McGinty.)
Resistance issues
He said producers need to be ready to go early in the season. Identifying key problem weeds is essential. He cited pigweed, common waterhemp and careless weed as resistance challenges.
“Pigweed and waterhemp are prolific seed producers,” McGinty said. “One female plant can producer 200,000 or more seed and may exceed one million under favorable conditions.”
He said these weeds have shown resistance to atrazine, glyphosate, and ALS herbicides in South Texas.
He said pre-plant incorporated/preemergence herbicides are critical in managing these weeds. In cotton, he recommends a preplant/pre-plant incorporated application with yellow herbicides. He would add a preemergence application of Cotoran/Caparol plus a group 15 product. In sorghum, he recommends atrazine plus a group 15 herbicide. “We may have mesotrione as an option in the near future.”
McGinty recommends a postemergence application of glufosinate/2,4-D/dicamba for cotton. For sorghum, he recommends atrazine plus Huskie/Starane NXT.
Other problem weeds
False ragweed, a challenging warm-season annual, germinates from 48 to 97 degrees Fahrenheit and produces 15,000 to 20,000 seed. “False ragweed is resistant to glyphosate, atrazine and paraquat, as documented in South Texas,” McGinty said.
Control should start with a pre-plant burndown. “Sharpen is an easy option in grain,” he said. “Glufosinate is good for cotton.”
Pre-plant incorporated and preemergence herbicides for false ragweed control in cotton include a preemergence option with Cotoran/Caparol plus a group 15 product. For grain, he recommends atrazine plus a group 15 and perhaps mesotrione soon.
Postemergence recommends include:
Cotton, “primarily glufosinate. Auxins are only effective on very small seedlings.”
Corn, glufosinate.
Sorghum, atrazine plus Huskie/Starane NXT.
Texas panicum is a tough-to-manage, warm season grass, “McGinty said. “It’s tougher to control than other annual panicums.
“Control is no problem in cotton and corn,” McGinty said. “We have plenty of options. It’s different for grain sorghum, and we need to consider managing Texas panicum with rotation or herbicide tolerant grain sorghum hybrids.”
He offered several options including Inzen from Corteva. “Inzen provides very good control of small Texas panicum, postemergence with Zest,” he said. Inzen offers no soil activity.
Igrowth, from Advanta is imidazolinone tolerant. “It provides good control of small Texas panicum, postemergence with Imiflex. Preemergence control of panicum is similar to a group 15,” he said.
Double Team, from S&W is ACC-ase tolerant, with “excellent grass control, postemergence with First Act.” Double Team has no soil activity.
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McGinty said Pennsylvania pellitory, a cool-season annual, may become “a major issue after a few years of no-till or strip-till management. It will mature at cotton or grain planting time and is difficult to control with any herbicide. Evaluation of herbicides is underway.”
McGinty said field residue can affect herbicide activity, but the South Texas climate typically “burns up residue quickly. We see adequate reason to treat and prevent weed emergence,” he said.
He also cautioned producers about weed escapes. “Some applications will burn the top of the weeds but will not get the lower canopy.” Those escapes often survive and produce seed that add to the weed seed bank in coming years.
He said maximum weed height for Liberty to be effective is 3 to 4 inches. “We see a significant difference in control on 4-inch weeds compared to 8-inches or 16-inches.”
McGinty said controlling weeds in conservation tillage systems comes with new challenges but is possible. “Timing is critical,” he said.
To view the workshop in its entirety, visit https://youtu.be/dWX5usx7LoE.
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