Oxadiazon Absorption, Translocation, and Metabolism in Rice (Oryza sativa) and Barnyardgrass (Echinochloa crus-galli)

The mode of action and selectivity of oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] were investigated in tolerant rice (Oryza sativaL.) and susceptible barnyardgrass [Echinochloa crus-galli(L.) Beauv. ♯3ECHCG]. Oxadiazon produced only brown spots on the foliage of rice plants at higher rates (> 500 ppmv), while LC50for barnyardgrass was 250 ppmv. Translocation of14C-oxadiazon from the treated leaf was minimal in both species; after 7 days, about 2 and 3% of applied14C translocated in rice and barnyardgrass, respectively. In rice,14C recovered in water and chloroform washings of the treated leaf was 25% in each and in barnyardgrass, 20 and 18%, respectively. After water and chloroform washings,14C-oxadiazon present in the treated leaf of barnyardgrass and rice was 36 and 26%, respectively. In rice and barnyardgrass, unaltered14C-oxadiazon represented 86 and 79% of applied14C, respectively, 7 days after application. In barnyardgrass 7 days after foliar application, oxadiazon inhibited14CO2fixation and the export of fixed carbon. The effects were less marked in rice.