Crop Loss Aftermath Spells Challenge for
Weed Management in Secondary Crops
Friday, June 20, 2014 By Mary Jane Buerkle
Resistant weeds, drought and now rainfall all have combined to create a "perfect storm" of sorts for some cotton producers who now need to plant secondary crops after hail or wind destruction.
For the past couple of years, as glyphosate-resistant Palmer amaranth has appeared on the High Plains, experts have been urging producers to take steps to tackle the problem by mixing "modes of action." Cotton producers increasingly have returned to using both pre-plant and pre-emergent herbicides, a practice popular before new technologies came along and allowed them to move away from residual herbicides, such as Prowl or trifluralin. However, these herbicides can cause damage to sorghum and corn, and for producers facing the challenge of replanting from cotton to those crops, that's just one more thing for them to consider.
Dr. Wayne Keeling with Texas A&M AgriLife Research said the amount of risk depends on how well producers incorporated the materials.
"If you used higher rates for a particular soil type and did a good job incorporating the yellow herbicide, that's where there would be more challenges," Keeling said, noting that the trend actually has gone to less incorporation.
Keeling said it's important for producers to use "buster planting" to ensure that new secondary crop seed gets into untreated areas, reducing the chance of injury from residual herbicides.
"Farmers need to bust out and get below the herbicide layer," he said.
Dr. Peter Dotray, weed scientist with Texas AgriLife Research and the Department of Plant and Soil Science at Texas Tech, said that materials such as trifluralin or Prowl are very tightly bound to the soil and because of their extremely low water solubility, don't move much when it rains. However, intense rainfall that moves soil may cause these herbicides to move because of that tight bond.
Herbicides put out behind the planter such as Dual, Direx, or Cotoran, generally are a little more water-soluble than pre-plant herbicides, Keeling said, but still are likely to be in place even with the rainfall.
Dotray noted that Staple, used either pre- or early-post, is more mobile in the soil and more injurious to sorghum or corn being planted. In fact, AgriLife Extension and Research experts recommend not to plant sorghum on ground where Staple has been used, regardless of the planting method. The earlier in the season that herbicides are applied, the less the labeled rate used, good soil moisture, band versus broadcast, and tillage will all play a role in dissipating the herbicide. With Staple, the biggest factor is time. A minimum of 10 months is needed prior to planting crops like sorghum, corn, sunflower, and sesame.
"Staple herbicide will move," Dotray said. "With the good rains, we don't know exactly where it is. If a grower busts out like he thinks he needs to, he might be putting seed exactly where the herbicide is. We're not sure what the next best answer is on that."
Keeling said that in conservation-tillage fields where producers applied trifluralin or Prowl and simply planted and watered it in, there is less chance of a problem. The challenge is greater in conventional-tillage fields.
Producers replanting back to sorghum should consider weed control of that crop as well, Keeling said.
"You need to have a good residual program like you did for cotton," Keeling said. "There are good post-emergent options out there, but not a substitute for a good pre-emergent program."
These issues and more are addressed in Texas A&M AgriLife Extension's recent release of their replant decision guide, "2014 Alternative Crop Options After Failed Cotton and Late-Season Crop Planting for the Texas South Plains." This document is available for download at http://www.plainscotton.org.
Producers also are urged to consult the chemical labels or their chemical dealer.
The Texas Department of Agriculture has submitted a Section 18 Emergency Specific Exemption request to the Environmental Protection Agency to use propazine to treat up to 3,000,000 acres of cotton to control glyphosate-resistant Palmer amaranth.
The request is now up for public comment, and comments must be received on or before July 3.
PCG urges all members to submit comments that are positive in nature with regard to this request from TDA. Both TDA and PCG believe that this emergency-specific exemption is urgently needed to control glyphosate-resistant Palmer amaranth.
Submit your comments, identified by docket identification (ID) number EPA-HQ-OPP-2014-0419, by one of the following methods:
Online: Federal eRulemaking Portal: http://www.regulations.gov. Follow the online instructions for submitting comments. Do not submit electronically any information you consider to be Confidential Business Information or other information whose disclosure is restricted by statute. The direct link can be found online at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2014-0419-0001; click the "Comment Now!" button on the right.
Mail: OPP Docket, Environmental Protection Agency Docket Center (EPA/DC), (28221T), 1200 Pennsylvania Ave. NW., Washington, DC 20460-0001.
Hand Delivery: To make special arrangements for hand delivery or delivery of boxed information, please follow the instructions at http://www.epa.gov/dockets/contacts.html.