Weed scientists report new herbicide resistant weed populations

July 12, 2010
Contact Information:

Bob Scott, Cooperative Extension Service, Lonoke. 501-676-3124, bscott@uaex.edu

Jason Norsworthy, Arkansas Agricultural Experiment Station, Fayetteville, 479-575-8740, jnorswor@uark.edu

Howell Medders, Division of Agriculture Communications, 479-575-5647, hmedders@uark.edu

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STUTTGART, Ark. -- Research and recommendations on managing the growing problem of herbicide-resistant weeds in rice and its usual companion crop, soybeans, will be presented at the Arkansas Rice Expo Aug. 4 at the University of Arkansas Division of Agriculture's Rice Research and Extension Center.

Rice flatsedge and smallflower umbrella sedge are the latest rice weeds with confirmed populations that are resistant to the widely used ALS herbicides, Division of Agriculture weed scientist Jason Norsworthy said. He added that ALS-resistant barnyardgrass, the main weed problem in rice, is continuing to spread.

Norsworthy and extension weed scientist Bob Scott will show research plots and recommend best practices for avoiding and managing resistant weed populations, including pigweed in soybeans.

ALS refers to the acetolactate synthase (ALS) inhibitor mode of action in several widely used herbicides. In the sedges, plants that can survive spraying by one ALS herbicide appear resistant to all herbicides with that mode of action, Norsworthy said.

The weed scientists generally prescribe a multi-faceted strategy, including crop rotation, as the most effective way to prevent and manage herbicide resistant weeds.

"We are running out of modes of action. There are not a lot of bullets left in the gun," Norsworthy said. He added that spring floods might have worsened resistant weed problems due to weed seed floating from one field or farm to another.

Scott and Norsworthy will review two new rice herbicides, Permit Plus and League, and recommend ways to control broadleaf weeds on levees without spraying 2,4-D herbicides, which were banned in 15 counties for use after April 15 due to the risk of drift damage to nearby crops.

The Rice Expo Aug. 4 will open with registration at 9:30 a.m. Visitors can choose two from five tours, from 10 a.m. to noon, on:

-- Rice varieties, hybrid breeding, diseases;

-- Clearfield rotations, rice weeds, pigweed in soybeans;

-- Nitrogen management and environmental studies;

-- Soybean varieties and diseases, soybean and rice insects; or

-- USDA-ARS research.

Chuck Barrett, the "Voice of the Razorbacks," will be the lunch speaker. Activities include a trade show, equipment demonstrations and family and youth activities and booths with trap shooting, climbing wall, archery, ATV safety and more. Directions and a schedule are at http://aaes.uark.edu/rice.html.