JOHNSONGRASS (SORGHUM-HALEPENSE) CONTROL WITH IMAZETHAPYR AND HALOXYFOP IN CONVENTIONAL AND VERTICAL-TILLED SOYBEAN (GLYCINE-MAX)

Field studies in conventional and vertical-tilled soybeans were conduc ted in 1992/93 and 1993/94 at four locations in Argentina to compare t he efficacy of imazethapyr and haloxyfop for johnsongrass control, Con trol was evaluated by measuring frequency of johnsongrass-infested are as at the beginning of the 1992/93 and 1993/94 growing seasons, Relati ve johnsongrass leaf area and number of rhizome phytomers within infes ted areas also was evaluated, Herbicide application reduced frequency of infested areas in the 1992/93 growing season, Frequency of infested areas increased in check plots. No differences were found among herbi cide treatments, suggesting that the effect of imazethapyr was as high as that observed for specific graminicides. Reduction in frequency of infested areas caused by herbicide treatments was accompanied to some extent by a decrease in intensity of infestation within infested patc hes assessed by measuring johnsongrass relative leaf area, Phytomer po pulation levels, on the other hand, were reduced only after two consec utive years of herbicide application, No differences were found among herbicide treatments in terms of impact on both measures of weed abund ance, Johnsongrass responded similarly to all treatments regardless of tillage system.