The sugarcane varieties ‘LCP 85-384’, ‘HoCP 85-845’, and ‘LCP 82-089’ were treated in the plant cane crop (first production year) with various combinations of azafeniden preemergence (PRE) at 0.56 or 0.84 kg ai/ha after planting in September/October, postemergence (POST) at 0.56 kg/ha in spring (March), and semidirected at 0.42 kg/ha after the final cultivation at layby in May. In the first ratoon crop (second production year) azafeniden was reapplied in spring and at layby. Herbicide programs were compared with the standard program of atrazine plus pendimethalin PRE after planting, POST applications of diuron plus pendimethalin in spring, and atrazine plus pendimethalin semidirected at layby. Crop injury was negligible for all herbicide treatments applied after planting. Azafeniden injured sugarcane 30 to 33% when applied POST in spring, and injury was most severe in plant cane and first ratoon HoCP 85-845 when they were considerably taller and had more foliage at application compared with the other varieties. Injury from azafeniden following layby application ranged from 9 to 19% in plant cane and first ratoon crops. Multiple applications of azafeniden during the 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.

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 postemergence 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/ha 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.