Evaluating Weed Control Efficacy of Microencapsulated EPTC and Trifluralin Herbicides under Greenhouse Condition

In conventional formulations such as emulsifiable concentrates (EC), wettable powders, soluble liquids, etc., complete availability of the active agent is usually considered immediate or rapid following usage. Application rates of these formulations of pesticides are greater than the minimum threshold concentration to counter losses from sorption, volatilization, photodecomposition, microbial and chemical degradation, and leaching. Controlled-release technology for pesticides could reduce environmental damage and increase efficiency by enhancement of delivery to the site of action. This survey was conducted to determine the possibility of EPTC and trifluralin efficiency improvement by using microencapsulated formulation (MC) that were first synthesized in Iran.

Two separated greenhouse experiments were conducted in Tirtash Research and Education Center (Mazandaran–Iran) in 2014. The experiments were carried out in a factorial arrangement based on a randomized complete block design with three replications. The Microencapsulated formulation of EPTC and trifluralin herbicides were compared with emulsifiable concentrate formulation (Eradicane 82% and Treflan 48%) in 0 (control), 25, 50, 75 and 100 percent of active ingredient (a.i.) (4.92 and 1.2 kg a.i./ha, recommended doses for EPTC and trifluralin, respectively). For this purpose, the soil of pots were infested with the seed of Green foxtail (Setaria viridis) and Redroot pigweed (Amaranthus retroflaxus). The responses of weeds to treatments, specifically seedling number, were analyzed using ANOVA tests, non-linear regression, and fitting to three parameters of Weibull and log-logistic equations. This analysis was based on Akaike's Information Criterion, Residual Standard Error, and Lack-of-Fit Test indices in the R3.4.1 program. The effective dose were determined for 10, 50 and 90 percent of weed control (ED10, ED50 and ED90, respectively). Relative potency index (R) of formulation types were determined by divided ED50 of EC into MC formulations.

According to the results of the experiments, the formulation type had a significant effect on the weed numbers. The MC formulations of EPTC increased Green foxtail and Redroot pigweed control efficiencies. The ED10, ED50 and ED90 decreased from 0.72, 2.94 and 7.18 kg a.i.ha-1 in the EC to 0.41, 1.87 and 4.89 kg a.i.ha-1 in the MC formulation for Green foxtail and 1.08, 3.29 and 10.02 kg a.i.ha-1 in the EC to 0.57, 2.36 and 9.67 kg a.i.ha-1 in the MC formulation for Redroot pigweed. The R index of EPTC in Green foxtail and Redroot pigweed control were 1.57 and 1.39, respectively. Weed control increased as trifluralin dosage increased in both of the formulation types, although in higher doses of the MC, weed control efficiency increased more than the EC formulation. So the efficiency of the MC formulations depended on application dosages. The ED10, ED50 and ED90 of Green foxtail were 0.14, 0.55 and 1.27 kg a.i.ha-1 in the EC and 0.19, 0.52 and 0.98 kg a.i.ha-1 in the MC formulation. The ED10, ED50 and ED90 of Redroot pigweed were 0.20, 0.64 and 2.02 kg a.i.ha-1 in the EC and 0.26, 0.56 and 1.19 kg a.i.ha-1 in the MC formulation. So that the R index of trifluralin in Green foxtail and Redroot pigweed control were 1.05 and 1.14, respectively. The dependency of trifluralin behavior to applied microcapsule dose may be connected to capture of herbicide in microcapsule particles which it causes reduction of bioavailability of herbicide in soil lower than the threshold doses of injury level. Whiles under this experimental conditions, the herbicides are less affected by degrading agents and therefore have less opportunity to express the advantages of MC formulation. Whereas the field studies results showed that the 50% of the recommended dosage of MC formulation had same efficiency as 75% of the recommended dosage of EC formulations (results were not published).

Microencapsulation is a versatile tool for product design and is successfully used in various sectors and for a variety of different product features. However, although lot of research has been performed, only relatively few developments have made it into products in the agrochemical area. For example 37 actives out of 908 listed in total in the pesticide manual, mainly insecticides, are described as being formulated as control solutions. While the development of this technology in agriculture can play an important role in preserving the environment and reducing the pollution caused by pesticides. The purpose of the application of controlled release formulations is the gradual release of herbicides in a suitable amount with maintaining efficiency in agronomic conditions. This type of formulation is a combination of the herbicide and associated material that releases effective material over a given period due to weed control. The results of this study showed that the R index of EPTC and trifluralin were 1.57 and 1.05 in Green foxtail, and 1.39 and 1.14 in Redroot pigweed control, respectively. So that the microcapsule formulation of EPTC and trifluralin herbicides increased the efficacy and reduced the application dose.