Phytotoxicity, absorption, translocation, and metabolism of root-applied norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone] in tolerant narrowleaf and susceptible broadleaf guineagrass (Panicum maximum Jacq. # PANMA) biotypes were examined under greenhouse and laboratory conditions. Dose response studies conducted in the greenhouse showed greater injury to the shoots of broadleaf than narrowleaf biotypes. 14C-norflurazon absorbed was 0.3 and 0.5% and 1.6 and 2.4% of that applied, 3 and 7 days after application for narrowleaf and broadleaf biotypes, respectively. Of the total radioactivity absorbed after 3 and 7 days, 70 and 76% and 57 and 61% were translocated to the shoots of susceptible and tolerant biotypes, respectively. Gas chromatographic analyses revealed that broadleaf shoots had 3.08 μg/g dry wt of the parent compound while its tolerant counterpart had 0.40 μg/g dry wt, 7 days after application. The toxic parent compound was metabolized more rapidly to its non-phytotoxic desmethyl analog by narrowleaf biotypes, thereby preventing its accumulation in the shoots. Differences in absorption, translocation, and metabolism were responsible for the differential response of the two biotypes of guineagrass.
