Effect of Vegetable Oils on the Surface Tension, Diffusion and Efficiency of Sethoxydim to Control Wild oat (Avena ludoviciana Durieu.)

During last century, population explosion has been pressing man to produce more supplies of food by consuming more energy in agroecosystems like applying chemical management strategies. herbicides have increasingly become a key component of weed management programs. In Iran, using herbicides led to increasing wheat yield about 20% and 22% in rainfed and irrigated farms respectively (20). Nonetheless, herbicides have also a negative impact on environment. A tool for reducing the herbicide usage which allows to decreasing their cost and side effects is the use of adjuvants. They increase the effectiveness of the post-emergence herbicides. Some adjuvants have toxic effects on living organisms such as Polyethoxylated tallowamine adjuvants that they are very toxic in fairy shrimp (Thamnocephalus platyurus) (6). Vegetable oils are not phytotoxic and likely are degraded and metabolized quickly in the environment (8). Sethoxydim is an acetyl coenzyme A carboxylase (ACCase) inhibitor that is considered to be a key enzyme in lipid biosynthesis. Similar to other foliar applied herbicides, it need to be associated with an adjuvant for more effective control. Vegetable oils can be developed characteristics of sethoxydim solution such as surface tension and spry drop diffusion. Therefore, the objective of this research is to determine the effect of vegetable oils on the surface tension, diffusion and efficiency of sethoxydim to control wild oat (Avena ludoviciana Durieu.).
Materials and Metods: To evaluate the effect of vegetable oils on properties of sethoxydim solution, a series of experiments were separately conducted at Ferdowsi University of Mashhad and Khorasan Science and Technology Park in 2012. For evaluating the effect of vegetable oils on surface tension of distilled water and sethoxydim solution and the sethoxydim efficiency on wild oat control, three experiments were conducted as factorial based on completely randomized design. In other experiment the vegetable oils application on diffusion of sethoxydim was conducted also based on a completely randomized design. A K100 tensiometer was used to measure the surface tension of water and sethoxydim solution containing vegetable oils. For measuring the diffusion of sethoxydim solution containing vegetable oils, water sensitive paper was used. The surface changing color was evaluated by using MIP software. Wild oat seeds were collected from plants in the field near the research greenhouse at Ferdowsi University of Mashhad, Iran. They were dehulled and placed in 11 cm diameter Petri dishes on top of a single layer of filter paper (Whatman International, Maidstone, UK). Then, 10 mL of 0.2% KNO3 solution were added to each Petri dish and the seeds were incubated for 48 h at 4–5°C in the dark. The seeds then were germinated under temperature and relative humidity control conditions in the dark (16 h at 20°C and 8 h at 10°C, with 45% and 65% relative humidity, respectively). By this method, 92–98.5% of the seeds germinated. Ten germinated seed were planted in each 1.5 L plastic pot that was filled with a mixture of sand, clay loam soil, and peat (1:1:1; v/v/v). The pots were sub irrigated every 3 days. The seedlings were thinned to four per pot at the one leaf stage and 40 mL of a water-soluble N: P: K (20:20:20) fertilizer, at a concentration of 3 g of fertilizer per liter of tap water, were supplied to each pot.
The results showed that the use of vegetable oils except castor oil caused reduction in the surface tension of distilled water. About the surface tension of the sethoxydim solution, all vegetable oils significantly reduced surface tension. There is anegative relationship between surface tension of sethoxydim solution and efficiency of sethoxydim. Regression analysis results of the surface tension and spray deposit distribution on sensitive paper percent showed strong negative relationship them. Effects of adjuvants on herbicide surface tension have been showed by other researches. As judged by the ED50 and relative potential showed in table 3, all vegetable oils led to increased herbicide efficiency. Using adjuvants led to increasing performance of herbicide.
Using of vegetable oil can be reduced needed sethoxydim for controlling wild oat. Reducing surface tension of herbicide solution can be known as a main reason for improvement of herbicide efficiency in the presence of vegetable oils. Low surface tension lead to more distribution of herbicide solution on leaf surface and eventually increased herbicide absorption.