Optimizing the Efficacy of Mesosulfuron-methyl + Sulfosulfuron (Total)R Herbicide on Wild Oat (Avena Ludoviciana L.) Control Using Mineral Oils

Introduction: Nowadays, concerns about side-effects of herbicides on human health and environment leading to increase the cost of new herbicide registration or reduce the old herbicide efficacy. Surfactants could increase the efficacy of post-emergence herbicides, due to reduction of herbicide solution surface tension. Surfactants may improve the herbicide effects and hence, reduce the amount of used herbicide to achieve the same results and this decreases the cost of herbicide application and the environmental effects. Surfactants are used in order to optimize the herbicide leaf uptake. They prevent the herbicide crystallization on leaf surface, herbicide drift and light composition. They improve the water quality for herbicide application, reduce the contact angle of herbicide droplet and also they spread and stick the herbicide droplet on leaf surface and facilitate the herbicide penetration into leaf cuticle. Some of surfactants are herbicide modifier, extender, and sometimes are safener or synergist.This study was conducted in order to determine whether the efficacy of mesosulfuron-methyl+sulfosulfuron (TotalR) herbicide on Avena ludoviciana control, could be improved by adding mineral oil surfactants.Materials and Methods: In order to study the efficacy of different mineral oil surfactants in mixture with TotalR herbicide on Avena ludoviciana control, an experiment was conducted at research greenhouse, Faculty of Agriculture, Ferdowsi University of Mashhad, in 2012. The study was a factorial experiment based on Completely Randomized Block (CRB) design, with four replications. The treatments were different TotalR herbicide concentrations (0, 5.625, 11.25, 22.50, 33.75, 45 gr a.i. /hectare) as factor A and factor B was different surfactants (Adigor, Propel, Volk, Citogate, Frigate and D-actil at 1% and 2% (v/v)) and distilled water as control. The seeds from Avena ludoviciana populations were collected from cropping fields of Mashhad Agricultural and Natural Resources Research Center, and were stored at dark incubator 4±1oC, during 72 hours. Then, the seeds were dehulled and placed in petri dishes and incubated for 48 hours at 4-5oC in darkness for dormancy breaking. The seeds were sown in potting tray (3*3*5 cm) filled with moistened peat. The trays were transported to germinator with 16/8 hour day/night and 20/10oC temperature. One week after sowing, when the seedlings were at one leaf stage, ten seedlings were transplanted in each plastic pots, that filled by mixture of soil, humus and silt (1:1:1 v/v/v). The pots were placed in greenhouse, 27±5/18±5oC, day/night. The pots were irrigated 2 days intervals. After 1 week the plants were thinned to 5 seedlings in each pot. The treatments were applied at 5 leaves stage by using an overhead trolled sprayer (Matabi 121030 SuperAgro 20 L sprayer, equipped with an 8002 flat fan nozzle tip delivering 200 L/ha, 2 bar spray pressure). Four weeks after spraying, plant biomass in each pot was harvested and recorded as fresh weight. Then, the samples were oven-dried at 75oC for 48 hours to measure the dry matter. The surface tension was measured by capillarity method. Logistic dose-response curves was used to describe the plant response (Fresh weight and dry matter of Avena ludoviciana) against the dose of herbicide alone or in mixture with surfactants at 1 and 2% concentration. Data were analyzed by SAS software, and mean comparison was done by LSD test (P<5%).Results and Discussion: Results showed that, all surfactants reduced TotalR solution surface tension, significantly. Surface tension was reduced by Citogate, D-actil, Frigate, Volk, Propel, Adigor, respectively. ANOVA results also showed that different herbicide doses and surfactant type had significant effect on Avena Ludoviciana dry and fresh weight. When the logistic dose-response curve was fitted for the effect of Total® herbicide on Avena loduviciana dry matter and fresh weight, both of them showed the same trend. It was observed that addition of mineral oils to herbicide solution improved Avena ludoviciana control. ED10, ED50 and ED90 as the regression coefficients are 13.09, 17.05, 26.01 gr i.a./ha for fresh weight and 6.75, 15.87, 31.39 gr i.a./ha for dry matter, respectively. In presence of surfactants, ED10, ED50 and ED90 was reduced for Avena ludoviciana fresh weight and dry matter and this represent the surfactant effect on herbicide efficacy. Herbicide relative potential index was more than one, when surfactants were used in mix with herbicide. Addition of all surfactant increased the efficacy of herbicide in reducing avena biomass. The results also showed that, Adigor (2% concentration) improved the herbicide efficacy 4.37 and 2.24 based on fresh weight and dry matter. Generally, it is possible to rank the surfactants in order for their ability to enhance the efficacy of TotalR solution as Adigor, Propel, Volk, D-actil, Citogate and Frigate, respectively.Conclusion: It is concluded that surface tension reduction ability may not be a correct index for surfactant selection. The efficacy improvement of tested herbicide by using mineral oils, may be due to solubilizing, softening, and disrupting the leaf cuticular wax by petroleum-based oils, despite the surface tension reduction of herbicide solution. This process can improve retention and diffusion of active ingredient of herbicide into cuticular wax. Consequently, more active ingredient arrives to site of action and a subsequent increases the effectiveness of herbicide.Proper surfactant selection is a key factor for efficacious weed management via reducing herbicide rate, which is a main research priority. This research demonstrated that when surfactants were tank mixed with tested herbicide, the herbicidal efficacy on Avena ludoviana species significantly improved.