Application of Avadex BW or triallate {(S‐(2,3,3‐trichlorallyl)‐diisopropylthiocarbamate} to soils subject to water ponding or temporary flooding may present some problems in wild oat (Avena fatua L.) control. Both wild oat and domestic oat (Avena sativa L.) are susceptible to triallate. Laboratory incubations of triallatetreated soils at 25°C showed the response of domesticated oat (cultivar ‘Harmon') to triallate was related to soil moisture content and to the length of incubation time. Triallate activity decreased more slowly at a soil water content of 5% below field capacity than for incubations at field capacity. Triallate treated soils incubated under water saturation conditions generally retained a higher level of phytotoxicity than those incubated at moisture contents of field capacity or less. Soils containing trial late incubated at a moisture content mid‐way between saturation and field capacity did not differ in activity to those incubated at field capacity. These results suggest that with soil moisture contents at or above field capacity but not saturated, trial late in‐activation may be more rapid than at more normal moisture levels for agricultural soils.