Summary.An investigation was made of a now herbicide, 2–amino‐3–chloio‐1,4–naphthociuinone (ACNQ,), which appears to be promising for the control oiEchinochloa crus‐galli(L.) Beauv. in transplanted paddy rice Oryza sativaL.).In pot experiments in the glasshouse, seedlings ofEchinochloaat different stages of growth were killed by ACNQ, at doses equivalent to 2–4 kg/ha (applied as granules) if they were submerged, but not if the shoots emerged above water. Activity was increased more by raising the level of water in the pot than by increasing the dosage. Emergent rice seedlings were little affected by ACNQ, up to 8 kg/ha, and the observed selectivity is considered to be due mainly to differences in plant height in relation to depth of water.In laboratory experiments with rice seedlings grown without soil, the activity of ACNQ again increased with the depth of solution. Conversely, at a standard solution depth, there was a reduction in damage with advancing stage of growth, and the chemical had little effect once the leaf tip was above the solution surface.The rate of leaching of ACNQ. through a sandy soil was slow and, at a dose of 2 kg/ha, persistence was about 15 days.In evaluating new herbicides for paddy rice it is suggested that screening tests arc necessary on submerged as well as non‐submerged plants.Activité herbicide de la 2–amino‐3–chloro‐1,′4–naphtoquimne. I. Activité herbi
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