Grower Awareness of Glyphosate- Resistant Weeds and Resistance Management Strategies for Cotton Production Systems in Mississippi and North Carolina. S. B. Clewis 1, W. J. Everman 1, D. L. Jordan 1, J. W. Wilcut 1, D. R. Shaw 2, R. G. Wilson 3, W. G. Johnson 4, S. C. Weller 4, B. G. Young 5, and M. K. D. Owen 6 1 North Carolina State University, 2 Mississippi State University, 3 University of Nebraska, 4 Purdue University, 5 Southern Illinois University, and 6 Iowa State University.

Introduction Interest in academia, industry on long-term impact of intensive glyphosate usage on weed population shifts. A 6-state project assessing the long-term viability of Roundup Ready (RR) technology as a foundation for corn, cotton, and soybean production began in 2005 in Illinois, Iowa, Mississippi, Nebraska, and North Carolina. This talk today will focus on the starting point – survey of growers on cotton production.

Purpose of Roundup Ready Grower Survey What is the effect on weed species of 10 years of Roundup Ready cropping systems? Are we observing increased weed resistance to glyphosate? How do farmers perceive the problem of glyphosate resistance? What are they willing to do about it?

Survey Objectives 1.Characterize the historical utilization of Roundup Ready crops. 2.Discern herbicide use patterns. 3.Gain grower insight on the performance of glyphosate-based weed control systems. 4.Identify any practices which may lead to greater weed management challenges and/or to determine practices that may lead to sustainability.

Resistance Attitudes Awareness of the Potential for Glyphosate Resistance. Perception of Severity. Awareness of Resistance in their States. “Experience” of Resistance on their Farms. Willingness to Take Management Actions. Perception of Effectiveness of Resistance Management. Obstacles to Resistance Management.

Methods Grower lists were generated for: Illinois, Indiana, Iowa, Mississippi, Nebraska and North Carolina. Growers were randomly selected from Monsanto lists of trait licensees. Survey was conducted from Nov. ‘05 to Jan. ‘06 by a third party and academia. Cropping rotations varied by state; for example in MS and NC: – Continuous RR cotton. – Continuous RR soybean. – RR crop fb non-RR crop rotation.

Methods 1,195 total respondents (~200 per state). 95% confidence level with +/- 3.1%. Grower Requirements: – Still actively involved in farming. – Responsible for decision-making. – Not employed in crop protection or seed industry – Farming a minimum of 250 acres of soybean, cotton, or corn. – Planting a RR trait for minimum of 3 years.

Weed Resistance Continuous Roundup Ready Cotton Rotation Mississippi and North Carolina

Overall General Awareness of Resistance: Are you aware of the potential for weeds to develop resistance to glyphosate herbicides? 91% n = 97

Perception of Severity of Resistance Problem: How serious of a problem do you consider weed resistance to glyphosate herbicides in a continuous RR cotton rotation? |----45%----||----55%----| n = 97 (Use scale of 1 to 10)

Documented Glyphosate Awareness: Are you aware of any specific weeds in your state that have been documented to be resistant to glyphosate herbicide? 56% 64% n = 43n= 42

Resistant Weeds Documented in State: What specific weeds in your state have been documented as being resistant to glyphosate herbicides?

Sources of Learning About Weed Resistance: From what sources have you learned about weed resistance issues related to glyphosate herbicides?

Incidence of Personal Experience: Have you personally experienced any weeds on your farm that are resistant to glyphosate herbicides? n = 42n= 44 29% 25%

Specific Glyphosate-Resistant Weed Experience: What specific grasses or broadleaf weeds have you experienced on your farm?

Incidence of Taking Specific Action Taken: Are you doing anything specific in your weed management program to minimize the potential for weeds developing resistance to glyphosate on your farm? 62% n = 97 Including tillage, herbicides, or crop rotation

Specific Actions Taken: What specific actions are you taking to minimize weed resistance to glyphosate?

Weed Resistance Management Continuous Roundup Ready Cotton Rotation Mississippi and North Carolina

Overall Effectiveness of Resistance Management: As a way to manage potential glyphosate weed resistance, how effective do you consider _____? n = 163 Mississippi 57%

Overall Effectiveness of Resistance Management: As a way to manage potential glyphosate weed resistance, how effective do you consider _____? n = 182 North Carolina 62%

Resistance Management Obstacles: In terms of your farming operation, what are the major obstacles, if any, of ____ as a resistance management approach? Rotating herbicide chemistries Tillage Rotating crops Correct label rates and timely applications Using more than one herbicide chemistry (residual) Using more than one herbicide chemistry (POST-applied) Rotating to a non-RR crop Cost/economics (13%) Cost/economics (11%) Market prices (9%) Weather (20%) Cost/economics (23%) Cost/economics (20%) Weed control/effectiveness (21%) Number one obstacleResistance management option n = 97

Herbicide Application Continuous Roundup Ready Cotton Rotation Mississippi and North Carolina

Did you make a [insert] on the field/farm planted in continuous RR cotton this year? n = 97 8% 78% 40% Roundup formulation 74% Roundup formulation

How many applications of a glyphosate herbicide did you make in-crop or over-the-top of your continuous RR cotton in 2005? MS; n = 45 NC; n = 50

When did you apply a non-glyphosate herbicide this year? n = 97 69% 36%

Out of the last 3 years, including 2005, how many years, if any, have you applied a non-glyphosate herbicide? n = 43n= 49 60%52%

Over the past 3 years, what specific changes, if any, have you made to weed control or herbicide program?

Summary Continuous Roundup Ready Cotton Rotation Mississippi and North Carolina

Summary Crop rotations with continuous use of RR trait are more common than previously thought. Excellent awareness that glyphosate-resistant weeds exist in MS and NC (>90%). However, only 36% and 52%, respectively in MS and NC rated glyphosate resistance as a “very serious” problem. 63% of cotton growers were currently incorporating management programs to minimize herbicide resistance, but over 30% are using only glyphosate for control.

Conclusion MS and NC cotton growers recognized the potential for glyphosate resistance are willing to take steps to prevent glyphosate resistance. BUT the majority continue to use only glyphosate with minimal other inputs as their primary weed control year after year and don’t always recognize farming practices as resistance management strategies. – e.g. crop rotation

On-going Research Subset of surveyed farmers randomly selected for 4- year field study, pairing grower practices vs. resistance management recommendations. Goal: Identify how current recommendations to diversify weed management influence weed dynamics in different crop rotations. For example, in NC we are currently working on 30 on-farm sites. Weed population dynamics and field-scale economic data being collected.

Acknowledgements Monsanto – Jennifer Ralston, Rick Cole, Greg Elmore and David Heering Marketing Horizons – Bob Jasper