Reduction of Pesticide Pollution in Agricutural Soils by Using Controlled Release Formulations: Efficacy and Persistence Studies

The application rates for conventional herbicide formulations are generally greater than the recommended dosage, in order to overcome losses from degradation, leaching, volatilization, and sorption during the time needed for weed control. All these factors have encouraged the development of controlled release formulations (CRFs), which can reduce herbicides levels in the environment since less active ingredient need to be applied for maintaining the herbicidal efficacy. For soil applied herbicides, such as alachlor and norflurazon, the residual weed control is dependent on herbicide persistence and availability in soil. The present study describes the preparation, characterization and application to soil of CRFs containing the herbicides norflurazon and alachlor. Ethylcellulose formulations were obtained by a microencapsulation technique. The results of the in vitro release studies in water showed that a prolonged release of the herbicides to solution was successfully achieved by using ethylcellulose microspheres. In order to compare the herbicidal efficacy and persistence of norflurazon and alachlor applied as microencapsulated formulations with the commercial formulations, bioassay experiments were carried out. The formulations were applied as preemergence herbicides at 0.8 and 1.6 mg kg for norflurazon and alachlor, respectively, and oat (soils treated with alachlor) and soybean (soils treated with norflurazon) seeds were sown. The herbicide persistence in soil was studied sowing fresh seeds in each pot at different times after herbicides treatment. The results showed that the ethylcellulose microencapsulated formulations of norflurazon and alachlor protected the herbicides against their dissipation in soil, and remained biologically active longer than the commercial formulations.