This paper studied the effect of raw garlic extract on controlling Phytophthora capsici and pepper
Phytophthora blight by determining indoor toxicity and field efficacy．Results showed that raw garlic extracted from
different parts had good inhibitory effect on P. capsici．The higher concentration was，the stronger inhibition was．
The inhibitory effect of crud extracts from garlic bulb on the growth of P. capsici could reach 100.00% under 150.0
mg·mL^-1 concentration．As incubation time went on，the inhibition effect decreased gradually．The results of
pot experiment indicated that different concentration of all part of garlic extracts had certain control effect on P.
capsici．When the concentration of garlic extract from bulb reached 150 mg·mL^-1，and the controlling effect
could reach 59.38%．Results of GC-MS determination showed that there were 20，19 and 23 kinds of volatile
components in garlic root，stem and leaf，and bulb，mainly organic sulfur，accounting for over 90% of the
total volatile substance．But，there were distinct differences between composition and content．When pure
methylpropyl disulfide，diallyl sulfide，diallyl disulfide and diallyl trisulfide were added into the medium，the
growth of P. capsici was significantly inhibited．The best inhibition rate was 60.55% with 100 mg·L^-1 of diallyl
trithioether．Rotation and companion planting pepper with garlic could effectively control pepper Phytophthora
blight and the controlling effects were 59.81% and 62.09%，respectively．All these results indicated that garlic
volatile substance had a good application prospect in controlling P. capsici．