State plant board approves new pesticide crop systems

Fast Facts:

- Arkansas State Plant Board allows use of herbicides 2,4 D and dicamba with crops genetically modified for resistance
- Growers must await EPA approval for use of herbicides in Arkansas crop systems

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LITTLE ROCK -- Arkansas growers may have access to two new technologies for combating pigweed and other persistent broadleaf weeds as early as the 2015 growing season, after the Arkansas State Plant Board approved the use of two forms of genetically modified crops and their attendant pesticides for use in Arkansas.

On Thursday, board members approved the use of Dow Agroscience’s new Enlist Duo^TM (glyphosate, 2,4-D and choline) weed control system and Monsanto’s M1691 (dicamba) herbicides for weed control throughout the state after a public hearing on the proposed changes to the Arkansas regulations on pesticide classification.

Older formulations of 2,4-D, labeled for agricultural use have been banned from use between April 15 and Sept. 15 in 10 counties in northeast Arkansas where cotton is a major crop. The pesticide, applied during field preparation, can severely damage neighboring non-resistant cotton crops if it volatizes, drifts or otherwise moves “off target” from its intended field.

Similarly, soybeans, the state’s largest crop, are highly sensitive to dicamba, which is typically used prior to planting crops, or in corn or grain sorghum for weed control.

Monsanto’s “Roundup Ready® Xtend Crop System,” is intended to pair dicamba with glyphosate, glufosinate, or both — each being a broadleaf weed herbicide commercially known as Roundup or Liberty — with genetically modified strains of cotton and soybeans that are not harmed by either herbicide. In soybeans, the Roundup Ready® Xtend Crop System will combine dicamba and glyphosate.

Jason Norsworthy, professor of Crop, Soil and Environmental Science for the University of Arkansas System Division of Agriculture and the Bumpers College, said Palmer amaranth, commonly known as pigweed, has infested most cotton and soybean fields throughout Arkansas. Over the past 10-15 years, the weed became resistant to glyphosate, so the introduction of new crop traits paired with new pesticide formulations should help growers combat the weed, he said.

“The key to preventing the development of herbicide resistance is to keep diversity in those programs, from a weed-control standpoint,” Norsworthy said. “If we’re only using one effective herbicide once the weed emerges, it won’t be long before we’ll have resistance to that herbicide.”

Norsworthy said that 97 to 99 percent of all cotton, corn and soybeans grown in Arkansas are genetically modified for pesticide resistance.

Tom Barber, a weed scientist and associate professor of Crop, Soil and Environmental Science for the University of Arkansas System Division of Agriculture, said the board’s decision lays the groundwork for growers to begin introducing these new technologies in cotton and soybeans into their rotation, pending approval from the U.S. Environmental Protection Agency.

In October, the EPA approved the use of Dow’s Enlist Duo™ for use in 2,4-D-resistant corn and soybeans, known as the Enlist Duo^TM system, in six Midwestern states. The agency is now considering 10 southern states, including Arkansas.

Barber said he and other experts expect the EPA to approve the use of both the Dow and Monsanto systems in time for the 2015 growing season. However, he said, the introduction of both systems into Arkansas is likely to be on limited acreage, given the limited availability of genetically modified seeds for the systems.

Plant Board Chairman George Tidwell said adopting rules specific to the use of the two systems ahead of an EPA decision offered the state an opportunity to assert some degree of control over the systems’ use in Arkansas.

Use parameters

Six specific amendments to the state’s pesticide regulations outline conditions that must be met by growers using either of the new crop systems. They include avoiding application of either pesticide if the wind direction would likely endanger sensitive crops in neighboring fields or if the wind speed exceeds 10 miles per hour; a 400-foot buffer zone between application fields and neighboring non-resistant or sensitive crops when using specific Monsanto dicamba products; compliance with federal labels on pesticides if they are more restrictive than those issued by the Plant Board; requiring spray droplets to be at least 300 microns in diameter for Enlist Duo and at least 400 microns in diameter for Monsanto’s dicamba, and guidelines for unique tank mixes of multiple pesticides.

Norsworthy said the 400-foot was based on agricultural research conducted at U of A test facilities.

“A lot of this is small-scale research,” Norsworthy said. “We haven’t gone out and sprayed hundreds and hundreds of acres with dicamba or 2, 4-D. Once you do that, there’s probably greater risks than what we had in our small-plot research, but we have a pretty good understanding of how these compounds are going to behave, and what impact they are going to have on the adjacent crops.

Bill Robertson, a cotton agronomist with the U of A System Division of Agriculture in Newport, said the introduction of the new herbicides will be helpful to growers, but shouldn’t be looked at as a panacea.

“Being able to go over the top of cotton with dicamba, it’s not going to be a silver bullet, but it’s certainly going to be a valuable tool for us to have in our tool box,” Robertson said. “It’ll take the pressure off some of our other tools to keep them as viable options for many years to come.”

Mike Thompson, director of the Plant Board’s pesticide division, said his office had received no phone calls regarding either proposed rule change during the 30-day public comment period prior to Thursday’s hearing, and only one email and two letters addressing the changes. All three written comments were in support of adopting the changes, Thompson said.

Of the approximately half a dozen individuals who addressed the board during Thursday morning’s public comment period, only two raised concerns over adopting the new rule changes.

Legislative review

Thompson said the proposed rule changes would be reviewed Monday by the Rules and Regulations Committee of the Arkansas Legislature. Thompson said that historically, the committee had typically notified the board once changes had been reviewed before sending them on to the Secretary of State’s office, after which new rules would simply go into effect after 10 days, unless a given rule had a specified effective date.

In November, however, Arkansas voters approved an amendment to the state constitution, giving legislators greater authority to block a rule change. Thompson said he was not sure how this might affect Monday’s review of the proposed changes.

For more information on weed control, contact your county extension office, visit www.uaex.uada.edu or http://arkansascrops.com.

The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

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By Ryan McGeeney
The Cooperative Extension Service
U of A System Division of Agriculture

Media Contact: Ryan McGeeney
Content Specialist
U of A Division of Agriculture
Cooperative Extension Service
(501) 671-2120
rmcgeeney@uada.edu

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