Extended Abstract

Introduction

The use of appropriate adjuvants combined with proper nozzle selection has become a crucial and practical approach to enhancing weed control efficacy in agricultural systems. Spray efficacy is influenced not only by the herbicide dose but also by the physicochemical properties of the spray solution and the behavior of droplets on plant surfaces. One of the controllable factors in pesticide application is the size of the spray droplets; Increasing size can significantly reduce exo-drift. Additionally, the choice of nozzle type has a substantial impact on droplet size. Furthermore, viscosity-increasing adjuvants are considered effective in reducing volatility. These adjuvants can enhance the adhesion and spread ability of spray droplets while minimizing evaporation by altering the physical and chemical properties of the spray solution. Selecting the right adjuvant can effectively mitigate the negative effects of volatilization and improve both the safety and efficiency of herbicide application. Therefore, this study was conducted to evaluate the effects of natural gums and nozzle type on the physicochemical properties of the spray solution, as well as the biological efficacy of haloxyfop-R-methyl in controlling wild barley, a problematic weed species in cereal production systems.

Materials and Methods

In this study, twelve natural gums including sodium alginate, carboxymethyl cellulose, carrageenan, xanthan, guar, pectin, tragacanth, gum arabic, dextran, gellan, konjac, and Persian gum were evaluated along with a non-treated control. All gums were applied at a fixed concentration of 2 g L⁻¹ and combined with six herbicide doses (0, 9.45, 18.9, 37.8, 56.7, and 75.6 g a.i. ha⁻¹). Treatments were applied using three flat-fan nozzle types, including standard, drift-reducing, and air-induction nozzles, arranged in a factorial experiment based on a completely randomized design with three replications. To evaluate spray deposition, water-sensitive papers were used at the highest herbicide dose to determine percentage coverage. In addition, detailed laboratory measurements were performed to characterize key physicochemical properties of spray solutions, including viscosity, droplet contact angle on leaf surfaces, droplet spreading area, and evaporation time. These parameters were selected because they directly influence droplet retention, absorption potential, and ultimately herbicide performance on the target weed.

Results and Discussion

The results showed that konjac, cellulose, and gellan gums produced the highest viscosity values, measuring 89.8, 93.9, and 195.4 mPa·s-1, respectively. However, despite the significant increase in viscosity, there was no consistent improvement in herbicide effectiveness, indicating that viscosity alone is not a reliable indicator of biological performance in the field. In terms of droplet behavior, cellulose, xanthan, and guar gums resulted in the highest contact angles (approximately 65°), indicating reduced wettability for these treatments. Among all the treatments, guar gum also demonstrated the longest droplet evaporation time at 24 minutes, suggesting better droplet persistence on the leaf surface. In contrast, tragacanth and gellan gums showed lower contact angles (29° and 35°, respectively) and shorter evaporation times (8 and 9 minutes), which were generally linked to less favorable herbicide performance compared to the other treatments. The largest droplet spreading area was recorded with gellan gum (10.33 mm²) and dextran (9.63 mm²). Regarding spray deposition, the highest coverage of 44% was achieved when guar gum was combined with an air-induction nozzle. Dose-response analysis further revealed that the combination of xanthan with the air-induction nozzle and guar with the standard nozzle resulted in the lowest effective doses (ED₅₀) of 12.8 and 12.4 g a.i. ha⁻¹, respectively, and ED₉₀ of 33.17 and 34.9 g a.i. ha⁻¹, respectively. This suggests an improvement in herbicide efficiency under these specific treatments.

Conclusion

The combination of guar gum with the air-induction nozzle was found to be the most effective treatment for maximizing herbicide performance and improving weed control efficiency. In contrast, tragacanth gum consistently demonstrated the weakest performance across all nozzle types. Although gellan and xanthan gums did not directly enhance herbicide efficacy, their ability to increase spray viscosity and extend droplet evaporation time suggests they could be useful in hot and windy conditions, where droplet stability and persistence are crucial for enhancing spray performance.