Abstract
Selectivity mechanisms of diphenyl ether herbicide oxyfluorfen ((2-chloro-4-trifluoromethylphenyl)-3′-ethoxy-4′-nitro-phenyl ether) and chlomethoxynil (2, 4-dichlo-rophenyl-3′-methoxy-4′-nitrophenyl ether) in rice (Oryza sativa L.), barnyardgrass (Echinochloa oryzicola Vasing.), sorghum (Sorghum bicolar Moench), corn (Zea mays L.), tomato (Lycopersicon esculentum Mill), cabbage (Brassica oleracea L.), radish (Raphanus sativus L.), cucumber (Cucumis sativus L.), and buckwheat (Fiagopyrum esculentum Moench) were studied. Oxyfluorfen showed higher herbicidal activity to the plants than chlomethoxynil, and the plants absorbed more of the former. However, they metabolized 14C-chlomethoxynil more rapidly than 14C-oxyfluorfen. This greater absorption and lower metabolism of oxyfluorfen by the plants are considered main factors of its higher phytotoxicity.
In oxyfluorfen treatment, rice and corn were more tolerant and absorbed less of the herbicide than other plants. Tomato showed very severe damage and had the highest absorption rate. Degradation of 14C-oxyfluorfen in the plants was very limited. Absorption of oxyfluorfen by the plants is thus possibly one factor of its selectivity.
In chlomethoxynil treatment, rice and corn were more tolerant than other plants and showed the lowest absorption rate. Metabolism of 14C-chlomethoxynil was greatest in rice plants. Rates of absorption and metabolic activity of chlomethoxynil in these plants are considered to relate to its selectivity.
