Water-seeded rice response to clomazone

A study was conducted to evaluate rice cultivar tolerance to clomazone impregnated onto urea fertilizer and applied at the rice pegging (PEG) stage. A second study was conducted to evaluate rice injury, rice yield, and weed control with clomazone applied alone or in combination with bensulfuron or halosulfuron impregnated onto urea fertilizer applied at the PEG stage. Comparison treatments for weed control were also included in the study. In addition, a study was conducted to evaluate the safening potential of bensulfuron or halosulfuron applied with clomazone on rice grown hydroponically. In the cultivar tolerance study, rice foliar bleaching was 16 to 20% at 14 d after PEG (DAPEG) for long-grain Ahrent, Cheniere, Cocodrie, Cypress, Francis, and Wells when clomazone was impregnated onto urea, and 23 and 30% for medium-grain Bengal and short-grain Pirogue, respectively. Clomazone reduced the number of tillers/m2 21 DAPEG for all cultivars. Early season height reductions occurred for all cultivars; however, Pirogue was the only cultivar shorter than the nontreated at harvest. There were no yield reductions with regard to the medium and long-grain cultivars when compared with respective nontreated cultivars. Rice foliar bleaching decreased from 42% with a single application of clomazone to 23 to 30% at 7 DAPEG when bensulfuron or halosulfuron were impregnated with clomazone. Barnyardgrass and broadleaf signalgrass control did not decrease with the addition of bensulfuron or halosulfuron to clomazone. A single application of clomazone controlled rice flatsedge 0% at 28 DAPEG; however, rice flatsedge control was greater than 76% for all bensulfuron and halosulfuron treatments at 28 DAPEG. There were no differences in rice yield between any herbicide treatments. Bensulfuron and halosulfuron applied in a hydroponic solution, safened Bengal, Cocodrie, and Pirogue at 21 d after treatment from foliar bleaching caused by clomazone. Chlorophyll content of all three rice cultivars decreased regardless of clomazone treatment. Only chlorophyll content of Cocodrie was increased by the addition of bensulfuron and halosulfuron compared with a single application of clomazone