Efficacy of bio-surfactants and spray volume on performance of fenoxaprop-p-ethyl against Avena sterilis subsp. ludoviciana

Whether fenoxaprop-p-ethyl activity could be affected by the carrier volume and whether this relationship can be affected by two types of bio-surfactants, rhamnolipid and surfactin, was assessed under greenhouse conditions. Treatments consisted of herbicide dose (0, 18.75, 37.5, 56.25, 75, and 93.75 g ha-1), spray volume (60, 120, 240, and 480 L ha-1), surfactant type above, and surfactant concentration (0, 0.125, 0.25, 0.5, 1, 2, 4, and 8x critical micelle concentration (CMC). The dry matter of sterile oat was regressed over the doses of fenoxaprop-p-ethyl to obtain a dose causing 50% sterile oat control (ED50). Without surfactant, a 38% increase in the ED50 with increasing the spray volumes from 60 to 480 L ha-1 (44.7 and 72.1 g ha-1, respectively) revealed a negative relationship between fenoxaprop-p-ethyl activity and spray volume. In other words, a low-volume spray solution, creating smaller, more concentrated spray droplets, is necessary to get the optimal action of fenoxaprop-p-ethyl. This relationship could also be observed when both surfactants were used at 0.125 to 1x CMC. At 2 to 8x CMC, the relationship mode changed from negative to neutral for rhamnolipid, while it did not change for surfactin. This study shows that, unlike surfactin, rhamnolipid worked better at a low concentration in a low-volume spray solution to get the optimal action of fenoxaprop-p-ethyl.