Improving the Efficiency of EPTC Herbicide in Tobacco Weed Control by Microcapsule Formulation and Herbicide Extender

The effectiveness of herbicides is influenced not only by the active ingredients and their toxicity but also by the formulation of the herbicide. Conventional herbicide formulations include wettable powder and emulsifiable concentrate (EC). EC formulations are prepared by mixing the active ingredient with solvents and surfactants. However, these formulations can have negative phytotoxic effects due to hazardous solvents and can be unsafe for operators during application. As an alternative to EC formulations, capsule suspension (CS) formulation has been considered. EPTC is a thiocarbamate herbicide used to control the growth of germinating annual weeds, including broadleaves, grasses, and sedges, in crops such as tobacco in Iran. EPTC acts by inhibiting cuticle formation during the early stages of seedling growth. It is available in formulated products such as emulsifiable concentrate (EC) liquids containing up to 87.8% active ingredient and granular (G) formulations containing up to 25% active ingredient. However, there have been few studies on the production of microcapsule formulations of this herbicide. This experiment aimed to evaluate the weed control effectiveness of EPTC microcapsule formulation, which was synthesized for the first time in Iran. Additionally, the study examined the effect of the herbicide extender, Ammonium thiosulfate, at different doses and application methods.

To investigate the effectiveness of different herbicide formulations and application methods, a three-way factorial experiment was conducted in Tirtash Research and Education Center in Mazandaran province, Iran, during the 2014 growing season. The experiment followed a randomized complete design (CRD) with three replications.
The factors studied in the experiment were:
Herbicide formulation:
Emulsifiable concentrate formulation (Eradicane® EC 82%)
Emulsifiable concentrate formulation with Ammonium thiosulfate
Microcapsule formulation
Herbicide dose:
50% of the recommended active ingredient (2.46 kg a.i. ha-1)
75% of the recommended active ingredient (3.69 kg a.i. ha-1)
100% of the recommended active ingredient (4.92 kg a.i. ha-1)
Herbicide application method

Soil-incorporated pre-planting
Pre-planting
A control plot with no herbicide application was also included. Throughout the growing season, weed density, weed dry weight, and tobacco yield were measured. The relative weed control compared to the control treatment was used to evaluate the efficiency of the different treatments. The collected data was subjected to analysis of variance using Minitab (Version 18), and mean comparisons were performed using the honestly significant difference (HSD) test at a significance level of 0.05.

Based on the relative frequency of weeds, Setaria viridis L. and Amaranthus retroflexus L. were dominant species. The experimental results show the effects of formulation type, application dose and method of application on weed density and weed dry weight and tobacco yield were statistically significant difference. The microcapsule formulation increased weed control efficiency and tobacco yield significantly compared to EC formulation and the highest weed control performance and tobacco yield belong to the soil incorporated of microcapsule formulation with recommended dose.

The results indicated that the utilization of a microcapsule formulation allows for a 25% reduction in the application dose of the EPTC herbicide, without compromising weed control or tobacco yield. Consequently, there were no significant differences observed between applying 75% of the recommended dose using the microcapsule formulation and applying 100% of the recommended dose using the EC formulation, with or without the extender. Based on these findings, it is crucial to promptly mix the herbicide with the soil immediately after spraying in order to maintain the efficiency of EPTC. Furthermore, it was discovered that employing two-thirds of the recommended dose of the microcapsule formulation yields the same level of effectiveness as the recommended dose of other formulations. Additionally, incorporating the EPTC herbicide with soil in all formulations enhanced weed control efficacy. In contrast to previous research suggesting the positive impact of extender adjuvants such as ammonium thiosulfate on herbicide efficiency, this study did not observe similar effects. This discrepancy may be attributed to the varying soil and climatic conditions at the test site.