Summary The influence of water stress on the absorption and translocation of 14C‐labelled fenoxapropethyl and imazamthabenz‐methyl in Avena fatua L. (wild oat) was studied. The phytoioxicity to A. fatua of both herbicides with a droplet application was also examined under water stress conditions. The absorption of both fenoxaproethyl and imazamethabenz‐methyl was reduced by waler stress when the plants were harvested within 24 h after herbicide application. Up to 48 h after the application, the translocation out of the treated lamina of both herbicides, based on percentage of applied 14C. was reduced under water stress conditions. When havested 96 h after herbicide application, however, water stress no longer significantly affeaed the absorption and translocation of either herbicide. When the herbicides were applied as individual droplets, water stress reduced the phytotoxicity of fenoxaprop‐ethyl but not that of imazamethabenz‐methyl. It is concluded that the changes in herbieide absorption and translocation may not be the major physiological processes associated with differential whole‐plant response oi A faiua to fenoxaprop‐ethyl and imazamefhabenz‐methyl under water stress.

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Controlled environmental experiments were carried out to determine the phytotoxicity of several graminicides on wild oat (Avena futua L.) as influenced by combination of drought and temperature stress or drought and low relative humidity. Compared with unstressed conditions (20/15°C plus adequate soil moisture), imazamethabenz phytotoxicity to wild oat was reduced significantly when plants were exposed to a combination of drought and high temperature (30/20°C) stress. Imazamethabenz phytotoxicity was reduced almost as much by high temperature stress alone as by a combined temperature and drought stress. When herbicides were applied to wild oat plants subjected to drought alone or to drought plus high temperature, the observed reduction in phytotoxicity from greatest to least was: fenoxaprop ‫ס‬ diclofop > flamprop > imazamethabenz. Fenoxaprop performance was most inhibited by the combination of drought plus high temperature, although drought alone and to a lesser degree, high temperature alone, inhibited fenoxaprop action. High temperature had an adverse effect on the efficacy of fenoxaprop at lower application rates. Raising fenoxaprop application rates to 400 g ha −1 overcame the inhibition caused by high temperature alone but only partially alleviated the effect of drought combined with high temperature. When plants were grown under a low temperature regimen the imposition of drought stress had little effect on imazamethabenz phytotoxicity but did reduce fenoxaprop phytotoxicity. At 25/15°C drought reduced the phytotoxicity of fenoxaprop and diclofop greatly but had no significant impact on the performance of any of the herbicides examined, regardless of soil moisture regimen.

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