Preliminary evaluation of alternative methods for the application of carbofuran in adapted soils

Two methods of application of pesticides viz. (i) application of the chemical (carbofuran or furathiocarb, a carbofuran precursor) on seeds; and (ii) soil application of encapsulated formulations (Ca2+-, Al3+- and Fe3+-alginate beads) of carbofuran were evaluated for their abilities to cope with practical problems resulting from the accelerated degradation of carbofuran in adapted soils. In previously-untreated soil, the half-life of carbofuran applied as the pure compound, the commercial microgranule formulation and the encapsulated formulation, was 8 weeks or more under standardized conditions (18–22°C; 80% of the soil water retention capacity). The half-life of the carbofuran applied on seeds was only 2 weeks in this soil. In the previously-treated soil, the half-life of the pure active ingredient of carbofuran was <2 weeks, but increased to >3 weeks with some of the encapsulated formulations such as alginate-Fe3+ beads and alginate-Ca2+ beads co-formulated with the fungicide TMTD. There was some evidence that degradation occurred only after the active ingredient had diffused out of the beads. The persistence of furathiocarb and carbofuran applied on seeds was <5 days for all the seed treatments tested in the previously-untreated soil. Encapsulated chemicals in alginate beads were more promising than seed treatment in increasing their persistence in soils showing accelerated degradation. It is, however, necessary to check whether these kinds of formulations are still effective with respect to their insecticidal activity.