Persistência dos herbicidas imazethapyr e imazapic em solo de várzea sob diferentes sistemas de manejo

The mixture of herbicides imazethapyr and imazapic is used to control red rice in irrigated rice crops. However, such herbicides might persist on the soil for a long period causing phytotoxicity on susceptible rice grown in succession. The objective of this work was to determine the effect of different soil tillage systems during the off-season on the residual phytotoxicity of imazethapyr and imazapic on non tolerant rice. Herbicide residues caused phytotoxicity on susceptible rice with the highest values being registered 25 days after emergence and decreasing after this period until almost disappearing 60 days after emergence. Herbicide residues affected plant stand, number of sterns per m(2), number of panicles per m(2) and plant height, but did not affect grain yield. Soil movement decreased herbicide activity on the superficial soil layer (0-3 cm).