Vegetable oil characteristics enhance the phytotoxicity of pinoxaden and haloxyfop-R-methyl on littleseed canarygrass Phalaris minor Retz.

It is possible to increase the efficacy of herbicides by adding vegetable oils to the spray tank. In order to evaluate and study this fact a greenhouse study was conducted. Three vegetable oils (coconut, sesame and almond oils at 0.3% (volume/volume)) were applied to compare their influence on enhancing the efficacy of pinoxaden and haloxyfop-R-methyl in 2012. The experimental design was completely randomized design with six replications in a factorial arrangement for each herbicide. The treatments were two herbicides, three adjuvants + untreated or control. The two herbicides were pinoxaden and haloxyfop-R-methyl that were divided into six doses (0, 6, 12.5, 25, 50 and 100 percent of recommended doses) and applied with and without vegetable oils to control littleseed canary grass. Moreover, dose–response experiment was carried out for any applied herbicides. The results of experiment revealed that by adding all vegetable oils haloxyfop-R-methyl ester weed suppressing influence was increased more when it is compared to pinoxaden that was attributed to a positive relationship between oil receptivity and the high octanol–water partition coefficient of haloxyfop-R-methyl ester herbicide. Among evaluated vegetable oils, coconut oil owned highest ability to enhance the efficacy of two herbicides which is probably due to high saturated / unsaturated ratio of fatty acids. In addition to, the comparison of vegetable oils’ effects on efficacy of herbicides demonstrated that better performance of coconut oil is probably related to the existence of short-chain fatty acids in coconut oil particularly, Caprylic, Capric and Lauric.