Red morningglory (Ipomoea coccinea) control with sulfentrazone and azafeniden applied at layby in sugarcane (Saccharum spp.)

A field study was conducted over 2 yr to evaluate red morningglory control and sugarcane injury with herbicides applied below the sugarcane canopy in late May to early June following the layby cultivation. Rainfall to activate herbicides was received within the first 2 wk after application at the two sites in 1997, but not at the two sites in 1998. Red morningglory control for most herbicides 21 d after treatment (DAT) in both years was at least 90% and was attributed to post-emergence activity of the herbicides and limited weed reinfestation following cultivation and herbicide application. At 45 DAT, red morningglory control with sulfentrazone was maximized (87 to 100%) at 0.14 kg ai/ha at three of four sites. Control with azafeniden was less consistent and, to achieve the same level of control as for sulfentrazone, 0.42 kg ai/ha azafeniden was needed in 1997 and 0.84 kg/ba in 1998. The currently registered herbicides atrazine, diuron, metribuzin, and terbacil controlled red morningglory no more than 83%, 45 DAT at three of the four sites. Of these herbicides, terbacil was the least effective. Even in 1997 at one site when the herbicide was rainfall activated early, red morningglory control with sulfentrazone at 0.14 kg/ha and azafeniden at 0.42 kg/ha 45 DAT was still greater than with the currently registered herbicides. Sugarcane injury expressed as foliage discoloration 21 DAT was 7 to 18% for sulfentrazone at 0.14 kg/ha and 15 to 31% for azafeniden at 0.42 kg/ha. Plant recovery was rapid and none of the herbicide treatments evaluated reduced sugarcane stalk height or population in September.