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Glyphosate-Resistant Palmer amaranth in the Southeast

Culpepper, York, Marshall

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TABLE OF CONTENTS

Glyphosate-Resistant Palmer amaranth in the Southeast Distribution of Glyphosate-Resistant Palmer Amaranth - Southeastern US Distribution of Glyphosate-Resistant Palmer Amaranth - Southeastern US Distribution of Glyphosate-Resistant Palmer Amaranth - Southeastern US Distribution of Glyphosate-Resistant Palmer Amaranth - Southeastern US Distribution of Glyphosate-Resistant Palmer Amaranth - Southeastern US Georgia County Extension Survey Determining the Impact of GR Palmer on Cotton Production Glyphosate-Resistant Palmer amaranth infestation levels in Georgia Georgia County Extension Survey Georgia Counties with Severe GR Palmer amaranth Infestations Impact of GR Palmer amaranth in Georgia counties with severe infestations Impact of GR Palmer amaranth in Georgia counties with severe infestations Why?? Lack of herbicide activation in dryland production? May 2008 Rainfall Distribution in Tifton Most Palmer amaranth emerges from top 2.5 cm Tillage Palmer amaranth seedling density No Deep Tillage vs Deep Turned Cultivation Glyphosate 3 lb ae + Pyrithiobac 0.25 lb (Palmer 3 inch at time of application) Why?? Hand weeding In-field pollen movement Number of Seed Produced per Plant - Glyphosate-Resistant Weeds in US Why?? Dryland Conservation Tillage Georgia Cotton OVTs - 2008 Georgia Counties with Light to Moderate GR Palmer amaranth Infestations Impact of GR Palmer amaranth in Georgia counties with light to moderate infestations Impact of GR Palmer amaranth in Georgia counties with light to moderate infestations Glyphosate-resistant Palmer amaranth infestation levels in Georgia Impact of GR Palmer amaranth in Georgia counties with light to no infestations Cover crop Impact of GR Palmer amaranth in Georgia counties with light to no infestations Glyphosate-Resistant Palmer amaranth - 2006 vs 2008 Herbicide Expenses per Acre Prevention and Early Detection are Essential! What's replacing the glyphosate applications? Percent Acres Treated with MSMA Impact of GR Palmer on North Carolina and South Carolina Questions or Comments?

SLIDE CONTENTS

Glyphosate-resistant Palmer amaranth in the Southeast Culpepper, York, Marshall Georgia County Extension Survey Determining the Impact of GR Palmer on Cotton Production Survey sent to 20 counties during fall of 2008. Results reported with counties broken in three levels (severe, light to moderate, none to light). Glyphosate-resistant Palmer amaranth infestation levels in Georgia. Severe (>60% land infested) Light to moderate infestations (20 to 60% land infested) Light infestations (<20% land infested) Georgia County Extension Survey Survey sent to 20 counties during fall of 2008. Results reported with counties broken in three levels (severe, light to moderate, none to light). Results weighted by cotton acreage. Georgia Counties with Severe GR Palmer amaranth Infestations. Severe Impact of GR Palmer amaranth in Georgia counties with severe infestations.* 92 25 25 2.0 2.7 88 Acres (%) treated with yellow herbicide Acres (%) treated with additional residual herbicide Number of glyphosate applications *Average of Macon, Taylor, Sumpter, Schley, and Dooly counties 83 26 5 % acres 48 20 0 0 45 *Average of Macon, Taylor, Sumpter, Schley, and Dooly counties Strip-tillage Herbicide Incorp. Glufos. systems 0 Cultivation Hand weeding 0 Impact of GR Palmer amaranth in Georgia counties with severe infestations.* Why???? Reducing conservation tillage? Increasing tillage? Lack of herbicide activation in dryland production? May 2008 Rainfall Distribution in Tifton (CPES) Prostko 2009 0.33” 0.02” 1.4” Herbicide activated Most Palmer amaranth emerges from top 2.5 cm Palmer amaranth seedling density No Deep Tillage Deep Turned Prowl H20 + Reflex PRE; WeatherMax + Dual Magnum POST; Direx + MSMA Layby Glyphosate 3 lb ae + Pyrithiobac 0.25 lb (Palmer 3 inch at time of application) No cultivation Cultivation Why???? Reducing conservation tillage? Increasing tillage? Why so much hand weeding? In-field pollen movement 230 K 250 28 K 309 K Giant ragweed 450 K Number of Seed Produced per Plant Glyphosate-Resistant Weeds in US Ragweed = Harrison et al. 2001; johnsongrass = Warwick and Black (1983); horseweed = Regehr and Bazzaz (1979); waterhemp = Nordby and Hartzler (2004); Palmer amaranth = Macrae et al (2009). Johnson-grass Horseweed Waterhemp Palmer amaranth Why???? Reducing conservation tillage? Increasing tillage? Why so much hand weeding? Why switching to glufosinate based program? Dryland Conservation Tillage Pendimethalin + fomesafen PRE Glyphosate + S-metolachlor POST Diuron + MSMA PD Pendimethalin + fomesafen PRE Glufosinate + S-metolachlor POST Diuron + MSMA PD Georgia Cotton OVTs – 2008 Plains and Tifton Dryland Production Light to moderate infestations Georgia Counties with Light to Moderate GR Palmer amaranth Infestations. Impact of GR Palmer amaranth in Georgia counties with light to moderate infestations.* 95 61 75 1.8 2.2 95 Acres (%) treated with yellow herbicide Acres (%) treated with additional residual herbicide Number of glyphosate applications *Average of Crisp, Lee, and Wilcox counties. 45 5 % acres 45 25 0 0 35 Strip-tillage Glufosinatesystems Cultivation Hand weeding 0 Impact of GR Palmer amaranth in Georgia counties with light to moderate infestations.* *Average of Crisp, Lee, and Wilcox counties. Lighter infestations Glyphosate-resistant Palmer amaranth infestation levels in Georgia. 30 2 % acres 60 12 22 0 37 Strip-tillage Glufosinatesystems Cultivation Hand weeding 1 Impact of GR Palmer amaranth in Georgia counties with light to no infestations.* *Average of Randolf, Colquitt, Turner, Berrien, Cook, Pulaski, Seminole. Impact of GR Palmer amaranth in Georgia counties with light to no infestations.* 91 35 70 1.7 2.3 71 Acres (%) treated with yellow herbicide Acres (%) treated with additional residual herbicide Number of glyphosate applications *Average of Randolf, Colquitt, Turner, Berrien, Cook, Pulaski, Seminole. 2006 Glyphosate-Resistant Palmer amaranth 2008 Herbicide Expenses per Acre.* 33 52 *Average of 10 counties responding. Does not included cultivation and hand weeding expenses. $ Prevention and Early Detection are Essential!!!! What’s replacing the glyphosate applications? Averaged over all counties, glyphosate applications were reduced from 2.4 to 1.8 applications in crop. Some glufosinate in severely infested fields. Primarily conventional mixtures at layby including MSMA? Percent Acres Treated with MSMA. Georgia Cotton 2008* 15 15 *N = 90 (70% grower, 15% Extension, and 15% consultant). 34 9 16 11 Impact of GR Palmer on North Carolina and South Carolina % Change in Conserv. Tillage: 0 -5 % Glufosinate Systems: 1 5 % Cultivation: 3 5 % Hand weeding: 17 50 % A treated w/Yellow: 40 75 % A treated with add. Herb: 40 55 NC SC Questions or Comments?