The response of the sugarcane cultivars HoCP 91-555, HoCP 85-845, and LCP 85-384 to flumioxazin during the first (plant cane) and second (first ratoon) production years was evaluated within two identical experiments, the first starting in 2000 and the second in 2001. In the plant-cane crop, flumioxazin application timings were PRE immediately following planting, fall postemergence (FPOST) 6 wk after planting, early spring postemergence (ESPOST), postemergence-directed spray (PDS) following layby cultivation, and sequential applications of FPOST followed by ESPOST. During the first-ratoon crop, flumioxazin was applied ESPOST, late-spring (LSPOST), PDS following layby cultivation, and sequentially LSPOST followed by PDS. Flumioxazin injury to sugarcane consisted mainly of stunted growth and reddening and necrosis of treated leaves. In plant cane, injury was 28% 2 wk after treatment (WAT) when applied ESPOST in one experiment but less than 10% in the other, and was no more than 13% in either experiment at 6 WAT. In the first-ratoon crop, injury was around 15% when applied ESPOST in the first experiment, but no injury was observed 6 WAT. However, in the first ratoon, injury to all cultivars was 25 to 30% when following a LSPOST application. When applied as a PDS, injury was no more than 15% 4 WAT in either plant-cane or first-ratoon sugarcane. Stalk height was reduced 15 cm compared to the nontreated control when flumioxazin was applied as a sequential application (FPOST followed by ESPOST) in plant cane and by 23 cm (LSPOST followed by PDS) in first-ratoon sugarcane. In plant cane ESPOST applications of flumioxazin reduced sugar yield (9 to 28%) within all three cultivars used in this study in both experiments with only one exception. Sequential (FPOST followed by ESPOST) applications reduced sugar yield within all cultivars (6 to 37%). PDS applications at layby reduced yields (7 to 12%) in the first experiment, but not in the second experiment. In the first-ratoon crop, LSPOST applications of flumioxazin reduced sugar yield (7 to 11%), sequential flumioxazin applications (LSPOST followed by PDS) reduced sugar yields (8 to 19%), and PDS applications at layby did not reduce yield. It appears that there is little if any difference in tolerance to flumioxazin for the cultivars used in this experiment. To avoid risk of yield loss, flumioxazin should not be applied as an over-top POST treatment to weeds in actively growing sugarcane, and care should be taken to minimize spray contact with sugarcane leaves when applying flumioxazin as a PDS at layby.

Nomenclature: Flumioxazin; sugarcane, Saccharum interspecific hybrids, ‘LCP 85-384’, ‘HoCP 85-845’, and ‘HoCP 91-555’.

Additional index words: Crop injury, application timing.

Abbreviations: EXP1, experiment one; EXP2, experiment two; TRS, theoretically recoverable sugar; USDA-ARS, U.S. Department of Agriculture, Agricultural Research Service.