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ARS Home » Southeast Area » Dawson, Georgia » National Peanut Research Laboratory » Research » Publications at this Location » Publication #190591
Title: MANAGING TROPICAL SPIDERWORT (COMMELINA BENGHALENSIS) IN A TWENTY-FOUR ACRE ON-FARM COTTON TRIAL

Author
item DUFFIE, W - AUBURN UNIVERSITY
item CULPEPPER, A - AUBURN UNIVERSITY
item Faircloth, Wilson

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: 1/3/2005
Publication Date: 7/1/2005
Citation: v 21.

Interpretive Summary: none required.

Technical Abstract: Tropical spiderwort has recently become the most troublesome weed in Georgia cotton. Nearly all of Georgia=s cotton is glyphosate-resistant, and glyphosate is only marginally effective in controlling tropical spiderwort. A replicated 24-acre field experiment with individual plots being 12 rows by 1000 feet was conducted to evaluate the effectiveness of tropical spiderwort management programs using growers’ equipment and application timings. Cotton cultivar DPL 449 BG/RR was planted on April 27, 2004 in a dryland field naturally infested with tropical spiderwort in Terrell County, Georgia. Treatments included a factorial arrangement of three early POST over-the-top (POT) treatments and three layby directed treatments. POT treatments included Roundup WeatherMax (glyphosate) at 0.75 lb ae/A alone or mixed with Dual Magnum (S-metolachlor) at 8 or 16 oz/A. Layby treatments included WeatherMax at 0.75 lb/A alone or mixed with Valor (flumioxazin) at 1.5 oz/A or Valor at 1.5 oz/A plus Dual Magnum at 8 oz/A. POT applications were made when cotton was in the 5-leaf stage with a John Deer 6500 high-clearance sprayer at 12 GPA on May 17. Layby applications were precision-directed using a Red Ball hooded applicator broadcasting spray under the hoods and directing spray 3 inches up the cotton stem when cotton was in the 13-leaf stage on June 18. Layby applications were 7 to 10 days late because of uneven and small cotton heights and rainfall. Visual weed control and cotton injury were measured throughout the season. Additionally, tropical spiderwort plants were counted and measured three times within each plot using one square meter sample areas. Tropical spiderwort control main effects were significant for POT and layby options. Pooled over layby treatments amd at 3 weeks after applications, 49 tropical spiderwort plants were present in a square meter. Twenty-two percent of these plants were larger than two inches. Dual Magnum at either rate mixed with WeatherMax applied POT reduced tropical spiderwort stands to only 12 to 13 plants per square meter with 6% or less of these plants being larger than 2 inches. Size of the emerged spiderwort is often critical as control with the layby application is directly related to tropical spiderwort size at that time. Pooled over POT treatments, tropical spiderwort control at 12 days after layby was 59% when WeatherMax was applied alone. Valor or Valor plus Dual Magnum added to the WeatherMax improved control 23 to 32%. At 33 days after layby, Valor mixed with WeatherMax improved control 40% while Dual Magnum mixed with Valor plus WeatherMax further improved control 8%. Control at harvest was poor with all treatments. WeatherMax, WeatherMax plus Valor, and WeatherMax plus Valor plus Dual Magnum provided only 24, 42, and 50%, respectively, when pooled over POT treatments. WeatherMax at layby did not injure cotton. Valor mixed with WeatherMax injured cotton 17%, and Valor plus Dual Magnum mixed with WeatherMax injured cotton 33% at 33 days after layby. WetherMax plus Dual Magnum applied POT followed by WeatherMax plus Valor or WeatherMax plus Valor plus Dual Magnum provided 82 to 88% control at 33 days after layby and 53 to 56% control at harvest.