Red Morningglory (Ipomoea Coccinea L.) and Sugarcane Response to Soil-Applied Herbicides.

Abstract

Laboratory and greenhouse studies were conducted to determine if reported red morningglory (Ipomoea coccinea L.) control failures with atrazine in sugarcane are due to triazine-resistant mutants. Terminal fluorescence of leaf material from locations with and without a history of atrazine use increased after treatment with atrazine, indicating electron transport inhibition and hence, triazine susceptibility. Postemergence (POST) application of atrazine controlled plants from all populations at least 99%, supporting findings of the fluorescence assay. A field study was conducted to evaluate red morningglory control and sugarcane injury with herbicides applied at layby. At 45 days after treatment (DAT), control with sulfentrazone was maximized (87 to 100%) at 0.14 kg ai/ha in three of four experiments. To achieve the same level of control as for sulfentrazone, 0.42 and 0.84 kg ai/ha azafeniden was needed in 1997 and in 1998, respectively. Currently registered herbicides atrazine, diuron, metribuzin, and terbacil controlled red morningglory no more than 83% 45 DAT in three of four experiments. Sugarcane injury 21 DAT was 7 to 18% for sulfentrazone at 0.14 kg/ha and 15 to 31% for azafeniden at 0.42 kg/ha. None of the herbicide treatments evaluated reduced sugarcane stalk height or population in September. Response of the sugarcane varieties 'LCP 85-384', 'HoCP 85-845', and 'LCP 82-089' to multiple applications of azafeniden was evaluated in plant cane and first ratoon crops. Comparisons were made to a standard program consisting of atrazine plus pendimethalin preemergence (PRE) after-planting, POST application of diuron plus pendimethalin in spring, and atrazine plus pendimethalin semi-directed at layby. Crop injury was negligible for all herbicide treatments applied after-planting. Azafeniden injured sugarcane 30 to 33% when applied POST in spring (0.56 kg/ha), and recovery from injury was delayed for HoCP 85-845 when it was taller and had more foliage per plant at application compared with the other varieties. Injury from azafeniden following layby application (0.42 kg/ha) ranged from 9 to 19%. Multiple applications of azafeniden during plant cane and first ratoon years did not reduce stalk height, population, sugarcane yield, or sugar yield for any of the varieties when compared with the standard herbicide program.