Microorganisms antagonistic to plant pathogens are common
in soil and there have been many attempts to use them
for biological control of many diseases (Mehrotra and Caludius
1972; Turhan 1981; Hayashida et al. 1989; El-Abyad et al.
1993a, 19936; El-Shanshoury 1994). The herbicides may
stimulate the antagonists that suppress soil pathogens.
Populations of actinomycetes antagonistic to Pythium were
increased by application of trichloroacetate (Yegen and Heitefuss
1970). Kaufman (1964) observed that linuron and diuron
decreased the total number of Fusarium sp. and stimulated
other fungi known to be antagonistic to this pathogen. We
screened 15 streptomycete strains, isolated from cultivated
Egyptian soils, for their antagonistic activities. Both Streptomyces
corchorusii (synonym Streptomyces oliviaceoviridis)
and Streptomyces mutabilis (synonym Streptomyces rochei),
which were isolated from cultivated Egyptian soils and identified
by El-Shanshoury (1985), were recognized as active
antagonists against the Fusarium wilt and the bacterial wilt
pathogens of tomato. In this investigation, single applications