M. Freund et al., REDUCED FLURIDONE EFFICACY IN SOIL - A POSSIBLE CASE FOR REVERSIBLE MICROBIAL INACTIVATION, Soil biology & biochemistry, 26(6), 1994, pp. 689-694
A reduction in efficacy of the persistent herbicide fluridone has been
observed in soils with fluridone application history (FH soils). Flur
idone activity, as monitored by bioassay, persisted in FH soils for ca
1 week, whereas in fluridone non-history (FNH) soils phytotoxicity co
uld be observed even after 3 months of exposure. Incorporation of smal
l volumes of FH soil were sufficient to confer rapid loss of herbicida
l activity on larger, autoclaved FNH soil volumes. In FH soils exposed
to intensive antimicrobial treatments the activity of fluridone was r
estored to levels similar to those observed in FNH soils. Autoclaving
and to a lesser extent, other disinfestation or antimicrobial measures
(gamma irradiation, methyl bromide, several fungicides) used to treat
FH soils, exposed test plants to phytotoxic compounds even though the
herbicide was not re-applied to the soil. Fluridone adsorption coeffi
cients (K(a)) in FH and FNH soils were similar, suggesting that physic
al adsorption of the herbicide does not play a key role in the observe
d inactivation of fluridone in FH soil. The possibility of reversible
microbial inactivation of fluridone is discussed.