Ecotoxicological evaluations and potential applications of controlled release carbofuran formulations in lowland rice.

The laboratory efficacy of controlled release carbofuran formulations [GO 3012 and GO 3009 (15% a.i.)] against the brown planthopper, Nilaparvata lugens Stal, peaked between 10-20 days after treatment with mortality rates from 80 to 100% compared to the 25% mortality rate by conventional granule and persisted up to 60 days after treatment. Against the striped stem borer, less than 20% mortality rates were obtained. In the field, controlled release granules reduced rice whorl maggot damage up to 36 days compared to 28 days by conventional granule. The GO 3009 significantly reduced green leafhopper population at 90% to 49% reduction by conventional granule and was more effective against the stem borer attacks. The GO 3009 exerted a high degree of insect control of insect pests at the tillering stage while GO 3012 was active during the booting stage. Higher yield was obtained from lower rates of application with GO 3009 registering the highest yield at 38% above the control and 15% higher than the conventional formulation. The least natural enemy diversity value at the tillering stage occurred on GO 3009 and at the booting stage from GO 3012 plots. The indices of diversity of predators and parasitoids were not significantly different and that makeup of natural enemies was homogeneous in all treatments. Toxicity test of controlled release and conventional carbofuran showed the wolf spider, Lycosa pseudoannulata Boesemberg and Strand was sensitive to carbofuran regardless of formulation. Residues in whole grain were within the tolerance limit and therefore controlled release carbofuran formulations can safely be used in rice. A rapid initial burst followed by a steady release characterized the release of controlled release granules in the laboratory with the larger particle sized granules releasing more active ingredient than smaller granule. In the field, the release pattern showed a steady increase for the first few weeks and declined slowly as a function of aging time.