Date of Graduation

12-2012

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Plant Pathology

Advisor/Mentor

Scott, Robert C.

Committee Member

Norman, Richard J.

Second Committee Member

Norsworthy, Jason K.

Third Committee Member

Gbur, Edward E. Jr.

Keywords

Biolgical sciences; Cotton; Fomesafen; Glufosinate; Glyphosate-resistance; Palmer amaranth

Abstract

In the mid-2000's, glyphosate-resistant Palmer amaranth biotypes began to emerge in many southern states. In 2006, glyphosate-resistant Palmer amaranth was identified in a field in Mississippi County, Arkansas. A greenhouse experiment was conducted in 2008 to screen Palmer amaranth accessions, collected in this survey, for glyphosate resistance. Inflorescence were collected from a total of 276 plants from fields were glyphosate failure occurred, representing 74 accessions in 14 counties, including Clay, Craighead, Crittenden, Greene, Jackson, Jefferson, Lawrence, Lee, Mississippi, Phillips, Poinsett, Randolph, St. Francis, and White Counties. Eight of the 74 accessions did not produce viable seed. In the greenhouse, 32 of the 66 Palmer amaranth accessions screened were at least 10% glyphosate-resistant. Two counties (Lee and St. Francis) contained Palmer amaranth accessions that were greater than 80% glyphosate-resistant. Every accession tested had at least one survivor following glyphosate at 0.86 kg ae/ha. Three field experiments were conducted in 2006 and 2007 to determine if preplant-applied fomesafen and postemergence-applied glufosinate would provide control of Palmer amaranth without causing cotton injury. A total of, 28 preplant (PPL) and preemergence (PRE) herbicide treatments and 27 herbicide programs were evaluated for Palmer amaranth control. The 28 PPL and PRE treatments were also evaluated for cotton injury. The 28 PPL and PRE treatments were fomesafen, flumioxazin, fluometuron, prometryn, diuron, and pendimethalin applied at four preplant timings (21, 14, 7, and 0 days). The Liberty Link herbicide programs, utilized glufosinate, S-metolachlor, fomesafen, fluometuron, prometryn, flumioxazin, diuron, and pendimethalin to control Palmer amaranth. At 7 days after emergence (DAE) of cotton, fomesafen applied at 0.21 and 0.28 kg ai/ha, flumioxazin at 0.071 kg ai/ha, prometryn at 1.12 kg ai/ha, diuron at 0.56 kg ai/ha, and pendimethalin at 1.12 kg ai/ha applied at 21, 14, 7, and 0 DPP all controlled Palmer amaranth 90 to 100%. Fomesafen at 0.21 kg ai/ha and flumioxazin at 0.071 kg ai/ha applied at 0 days prior to planting (DPP) reduced stand by 22 and 58%, respectively, when compared to those same treatments applied 21 DPP. Application timing was the only significant factor to affect cotton yield in the PPL and PRE study.

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