Evaluation the Effect of some Vegetable Oils on Pinoxaden (Axial®) Efficacy in Little Canarygrass (Phalaris minor Retz.) Control

Abstract

Introduction: Adjuvants are used worldwide in order to improve the efficacy of foliage-applied pesticides and minimize the environmental damaging effects. It is generally agreed that there are two main ways by which adjuvants can enhance ultimate biological performance of herbicides. Initially, by increasing the amount of active ingredient retained by the target, and the second promoting their uptake. Materials and Methods: Therefore, a greenhouse experiment was conducted to detect a suitable adjuvant for pinoxaden herbicide against littleseed canarygrass. Experiment was done as factorial in completely randomized design with 12 replications in Research Greenhouse of Ferdowsi University of Mashhad in 1390. The treatments consisted herbicide factor in 6 levels (0, 2.81, 5.62, 11.25, 22.5 and 45 g a.i. h-1) and adjuvant at four levels (without adjuvant, coconut, sesame and almond oil as a vegetable oil at 0.5 percentages by volume (% v/v). Seeds treated by 98% sulfuric acid for a period of 6 minutes then were planted in trays that were filled with peat moss. Trays were irrigated daily. After emergence, seedlings were planted in pots. The spray treatment was done at three to four-leaf stage by using an overhead trolley sprayer (Matabi 121030 Super Agro 20 L sprayer; Agratech Services-Crop Spraying Equipment, Rossendale, UK), equipped with an 8002 flat fan nozzle tip delivering 200 L ha-1 at 2 bar spray pressure. Four weeks after spraying, the plants of the experimental units were harvested and oven-dried at 75°C for 48 h, then weighed. The greenhouse temperature varied from 18°C to 25 °C during the day and 14°C to 21°C at night. Results Discussion Analysis of variance indicated that usage of vegetable oils and pinoxaden herbicide affected littleseed canarygrass biomass significantly at 1%. The results of the average comparison also showed that with increasing of amount of herbicide littleseed canarygrass biomass decreased significantly. It seems, increasing the amount of herbicide enhanced herbicide concentration gradient and resulted in the effectiveness of pinoxaden herbicide on littleseed canary grass. In all treatments, concentration of 45 g active ingredient had the greatest effect. Results of adjuvant main effects also showed that the use of vegetable oils had significant positive impact on pinoxaden herbicides. Coconut, sesame and almond oils respectively had the best performance in increasing the efficacy of pinoxaden herbicide compared to control without the adjuvants. The average amount of biomass for coconut, sesame, almond oils and control without adjuvants were 1.21, 1.41, 1.48 and 1.65 grams, respectively. Based on results of the regression analysis and comparison of the mean (P≥ 0.05), all adjuvants increased pinoxaden herbicide efficacy. The amount of ED50 decreased and relative potency (R) increased. Data analysis showed that coconut oil increased pinoxaden herbicide efficacy more than other Adjuvants and ranking of other treatment was such as sesame oil> peanut oil> herbicide without additive. ED50 of usage coconut oil, sesame seeds, almonds and pinoxaden alone was 29.98, 35.62, 45.93 and 57.80 g a.i.h-1 respectively. Average dry weight for pinoxaden alone, peanut, sesame, coconut oil was 1.65, 1.48, 1.41 and 1.12 grams, respectively. Probably high ratio of saturated to unsaturated fatty acids is reason greater efficiency of coconut oil than other adjuvants. In addition to the above reasons, It seems to abundant of shorter fatty acids in sesame oil and particularly coconut oil (Caprylic 8:0, Capric 10:0 and Lauric 12:0) compared with almond oil enhanced efficacy of herbicides. Vegetable oils that have more saturate/un-saturate fatty acids ratio were more effective in increasing the performance of herbicides. Instance, coconut oil with highest amount of this ratio (11.8) had the most impact on performance of herbicides. A positive relationship existed between lack of oleic acid and effectiveness of herbicides. Coconut and sesame oils with smaller oleic acid amount increased herbicide performance more that almond oil. Conclusion: The results indicated that the relative potency of coconut oil has increased more than the other oils. All the adjuvants were effective in increasing the efficacy of the herbicide and it is recommended that after farm tests if these materials have positive effects, they are used to increase the effectiveness of the herbicide.