Document Type : Research Article
Authors
Department of Plant Production and Genetics, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran
10.22067/jpp.2025.91240.1213
Abstract
Introduction
Wild barley is an annual and winter weed belonging to the family Poaceae. It can occupy a wide range of habitats and its damage to some crops, especially wheat and rapeseed, has been reported. One of Iran’s most widely used herbicides is haloxyfop-R-methyl, used against narrow-leaved weeds such as wild barley in rapeseed, sugar beet, and orchard fields. Haloxyfop-R-methyl inhibits the activity of the enzyme acetyl-coenzyme A carboxylase in the fatty acid biosynthesis pathway, resulting in a disrupted membrane structure and killing treated weeds. Increasing reliance on herbicides, metabolic damage to crops, and the environmental consequences of herbicides have left no choice but to reduce consumption. One of the methods of reducing the consumption of herbicides is the use of surfactants. The purpose of this study was (1) to determine the most compatible surfactant type and concentration among three surfactants: cationic frigate, anionic dioctyl, and nonionic PCgate for use with haloxyfop-R-methyl against wild barley; (2) to determine their mechanism of action.
Materials and Methods
In a dose-response experiment conducted in the autumn of 2012 in the research greenhouse of Bu-Ali Sina University, the compatibility of adding 7 concentrations (0, 0.025, 0.05, 0.1, 0.2, 0.4, and 0.8% by volume) of 3 types of surfactants (nonionic PCgate, cationic frigate, and anionic dioctyl) to spray solutions containing 7 doses of haloxyfop-R-methyl (0, 3.375, 6.57, 13.5, 27, 54, and 108 g a.i. ha-1) against wild barley was investigated. At the same time, the solutions containing the maximum dose of herbicide were also sprayed on moisture-sensitive paper. Moreover, the solutions containing the maximum dose of herbicide (108 g a.i. ha-1) along with 7 concentrations (0, 0.025, 0.05, 0.1, 0.2, 0.4, and 0.8% v/v) of 3 types of the surfactants above were prepared to measure their surface tension by the hanging drop method, and the contact angle of the drop with the leaf surface, the wetted area of the leaf, and the duration of drop evaporation by placing a 5 μL drop of the solutions on wild barley’s upper and lower leaf surfaces, which were fixed horizontally.
Results
The critical micelle concentration of the surfactants was determined to be 0.1% v/v. The addition of surfactants to the spray solution caused a decrease in the droplet contact angle with the leaf surface, an increase in the wetted leaf area, a decrease in the droplet evaporation time, an increase in the spray coverage on the moisture-sensitive paper, a decrease in the spray droplet size, and an increase in the efficacy of haloxyfop-R-methyl against wild barley, all of which were dependent on the surfactant concentration. Surfactants at all concentrations significantly reduced the surface tension of the spray solutions. A negative relationship was observed between the efficacy of haloxyfop-R-methyl and the surface tension of the spray solution (R2 = 0.68). Without surfactant, 25.39 g a.i. ha-1 was required to control 50% of wild barley (ED50). Among the treatments, the lowest ED50 (18.4 g a.i. ha-1) was observed when dioctyl was added at 0.2% v/v to the spray solution. Without surfactant, 68 drops cm-2 were deposited on the moisture-sensitive paper. The highest droplet density (83 drops cm-2) was observed when dioctyl was added at 0.4% v/v to the spray solution. Except at 0.8% v/v, at other concentrations, the efficacy of PCgate and dioctyl in increasing the droplet density deposited on the moisture-sensitive paper was equal, and the efficacy of frigate in this regard was lower than the other two surfactants. Except at 0.8% v/v, the efficacy of frigate was lower than that of the other two surfactants in wetting the moisture-sensitive paper, and there was no difference between PCgate and dioctyl. Leaf surface (anterior and posterior) had no significant effect on the measured characteristics and did not interact with surfactant type and concentration. The lowest droplet contact angle (30°) was observed when dioctyl at 0.4 and 0.8% v/v to the spray solution. The droplet containing PCgate at 0.4 and 0.8% v/v (12.3 and 12.5 mm2, respectively) resulted in the highest leaf-wetted area. The droplet containing dioctyl evaporated faster than the droplet containing PCgate, and the droplet containing PCgate also evaporated faster than the droplet containing frigate.
Conclusions
The results of the present study indicate that PCgate, dioctyl, and frigate are compatible with haloxyfop-R-methyl, even at high concentrations (up to 0.8% v/v). However, a concentration of 0.2% v/v of the surfactants is recommended to avoid additional costs. The ability of the surfactants to improve haloxyfop-R-methyl efficacy against wild barley is as follows: dioctyl > PCgate > frigate. Therefore, dioctyl is a better choice for addition to the haloxyfop-R-methyl spray solution. In this study, it was proven that the surfactants improve the efficacy of the haloxyfop-R-methyl by increasing the spray deposition by reducing the size of the spray droplets and increasing the spread of the droplets on the leaf surface of wild barley. Also, it seems that PCgate has moisture-absorbing properties that reduce the droplet evaporation time, increasing the duration of herbicide absorption.
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