Controlled-release formulations of diuron were prepared in the laboratory using
the concept of physical matrix utilizing sodium alginate and kaolin. The release rates of
diuron from the formulations were determined by chemical assay and bioassay. In the
chemical assay, using high performance chromatography with UV detector, significant
differences in release rates between formulations were observed from 3 to 7 days after
the granules were placed into distilled water. The formulation having a 1:1 ratio of
alginate to kaolin with 1 mm granule size showed the fastest release of diuron while
release from the 2 mm granules was slower. The release of diuron from the
formulations reached a maximum level of 27% at 30 days after placement in water this
same rate of release was maintained up to 60 days after the treatment. Increasing the
proportion of kaolin to sodium alginate in the controlled-release formulation reduced the
release rate of active agent.
Bioassays were conducted in the glasshouse to study the release rates of diuron
using Brassica rapa seedlings as bioindicator. The controlled-release formulations
showed slower release than the conventional formulation at the beginning of the
treatments. At 3 weeks after treatment, there was no significant difference in the
mortality of the seedlings between the conventional formulation and controlled-release
formulations. However, the controlled-release formulations gave significantly higher
seedling mortality compared to the conventional formulation at 16 weeks after the
treatments. The same results were observed up to 24 weeks after the treatment when
the controlled-release formulations caused between 40 to 70% mortality, while the
conventional formulation treatment caused only 6% mortality. Among the controlledrelease
formulations, the A K-2 formulation (1:1, alginate to kaolin) was found to give the
best control with the highest percentage mortality of the seedlings
