Residue and bio-efficacy evaluation of controlled release formulations of metribuzin against weeds in wheat.

Controlled release formulations of metribuzin in polyvinyl chloride, (emulsion); carboxy methyl cellulose, CMC and carboxy methyl cellulose- kaolinite composite, CMC-KAO are reported. The MET-CMC-KAO-3 (T(9)) formulation provided a superior control (76.1%) of weeds in field grown wheat in comparison to metribuzin 75 DF (57.14%) at the dose (350 g a.i. ha(-1)) after 90 days of sowing. The treatment (T(9)) reduced the dry weight of the weed flora after 30 days of sowing (4.0 g m(-2)) and significantly superior over metribuzin 75 DF (6.0 g m(-2)) and control (17.72 g m(-2)). There were nil to negligible metribuzin residue in soil at harvest of wheat crop and were within prescribed limit of 10 mg L(-1) in drinking water (EPA).

Controlled release formulations of metribuzin: release kinetics in water and soil.

Controlled release (CR) formulations of metribuzin in Polyvinyl chloride [(PVC) (emulsion)], carboxy methyl cellulose (CMC), and carboxy methyl cellulose-kaolinite composite (CMC-KAO), are reported. Kinetics of its release in water and soil was studied in comparison with the commercial formulation (75 DF). Metribuzin from the commercial formulation became non-detectable after 35 days whereas it attained maxima between 35-49 days and became non-detectable after 63 days in the developed products. Amongst the CR formulations, the release in both water and soil was the fastest in CMC and slowest in PVC. The CMC-KAO composite reduced the rate of release as compared to CMC alone. The diffusion exponent (n value) of metribuzin in water and soil ranged from 0.515 to 0.745 and 0.662 to 1.296, respectively in the various formulations. The release was diffusion controlled with half release time (t(1/2)) from different controlled release matrices of 12.98 to 47.63 days in water and 16.90 to 51.79 days in soil. It was 3.25 and 4.66 days, respectively in the commercial formulation. The period of optimum availability of metribuzin in water and soil from controlled released formulations ranged from 15.09 to 31.68 and 17.99 to 34.72 days as against 5.03 and 8.80 days in the commercial formulation.

Controlled release formulations of acephate: water and soil release kinetics.

Controlled release formulations of insecticide acephate (O,S-dimethyl acetylphosphoramidothioate) have been prepared using commercially available polyvinyl chloride, carboxy methyl cellulose and carboxy methyl cellulose with kaolinite. Kinetics of acephate release in soil and water from the different formulations was studied in comparison with the commercially available formulation 75 DF. Release from the commercial formulation was faster than the new controlled pesticide release (CR) formulations. Addition of clay in the carboxy methyl cellulose matrix reduced the rate of release. The diffusion exponent (n value) of acephate in water and soil ranged from 0.462 to 0.875 and 0.420 to 0.547 respectively in the tested formulations. The release was diffusion controlled with a half release time (T(1/2)) of 2.97 to 52.41 days in water and 2.98 to 76.38 days in soil from different matrices. The maximum release of acephate in water and soil from controlled released formulations occurred between 6.33 to 36.34 and 12.49 to 29.09 days respectively. The results suggest that depending upon the polymer matrix used, the application rate of acephate can be optimized to achieve insect control at the desired level and period.

Pesticidal seed coats based on azadirachtin-A: release kinetics, storage life and performance.

BACKGROUND: Infestation of seeds by pests during storage leads to deterioration in quality. Seed coating is an effective option to overcome the menace. Unlike synthetic fungicidal seed coats, little is known of those based on botanicals. This study aims at developing azadirachtin-A-based pesticidal seed coats to maintain seed quality during storage. RESULTS: Polymer- and clay-based coats containing azadirachtin-A were prepared and evaluated for quality maintenance of soybean seed during storage. Gum acacia, gum tragacanth, rosin, ethyl cellulose, hydroxyethyl cellulose, polyethyl methacrylate, methyl cellulose, polyethylene glycol, polyvinyl chloride, polyvinyl acetate, polyvinyl pyrrolidone and Agrimer VA 6 polymers and the clay bentonite were used as carriers. The time for 50% release (t(1/2)) of azadirachtin-A into water from the seeds coated with the different coats ranged from 8.02 to 21.36 h. The half-life (T(1/2)) of azadirachtin-A in the coats on seed ranged from 4.37 to 11.22 months, as compared with 3.45 months in azadirachtin-A WP, showing an increase by a factor of nearly 1.3-3.3 over the latter. The coats apparently acted as a barrier to moisture to reduce azadirachtin-A degradation and prevented proliferation of storage fungi. Polyethyl methacrylate, polyvinyl acetate and polyvinyl pyrrolidone were significantly superior to the other polymers. Azadirachtin-A showed a significant positive correlation with seed germination and vigour, and negative correlation with moisture content. CONCLUSION: Effective polymeric carriers for seed coats based on azadirachtin-A are reported. These checked seed deterioration during storage by acting as a barrier to moisture and reduced the degradation of azadirachtin-A.