Bt, which is
the bacterium, Bacillus thuringiensis (sold as Dipel, Gnatrol, and Thuricide) is an effective
organic pesticide specific to caterpillars, fungus gnat and mosquito larvae.
The problem
is that Bt does not kill immediately, and therefore, gardeners may think the
product is ineffective. The bacterium produces a toxin that, when ingested,
causes gut paralysis and eventual death. The affected caterpillar will stop
feeding within hours of ingestion, but it may take a day or two to actually die.
In addition,
Bt rapidly degrades in sunlight. For best results, applications should be made
in the late afternoon. Most caterpillars feed after dusk anyway. Bt is especially effective against the green garden
looper which commonly attacks many vegetable crops and some ornamental crops, including ti and tropical foliage.
