ble, high-yielding cultivars with large numbers of
tillers, and the changes in cultural practices asso-
ciated with these cultivars, favor the development
of sheath blight and contribute greatly to the rapid
increase in the incidence and severity of this dis-
ease in rice-producing areas throughout the world
(Groth et al., 1991; Rush and Lee, 1992). Further-
more, environmental conditions such as low light,
cloudy days, high temperature and high relative
humidity also favor the disease (Ou, 1985). The
pathogen overwinters as soil-borne sclerotia and
mycelium in plant debris; these constitute the pri-
mary inoculum. Control of the pathogen is difficult
because of its ecological behavior, its extremely