This research was conducted to evaluate the suppression effect of extracts obtained from plant parts of Allium species using different extraction methods (water， boiling water， and ethanol) on crop pathogens and weeds. Pyricularia oryzae and Colletotrichum coccodes were inhibited 71% and 78% by 5% ethanol extract of onion (cv. Deosingihan)， respectively. The suppression of Pyricularia oryzae and Colletotrichum coccodes by ethanol extract of onion (cv. Deosingihan) was higher than other onion cultivar extracts (cvs. Sinseonhwang， Sunpower， Romang and Cheonjujeok). On the other hand， Pyricularia oryzae， Phytophthora cactorum， and Colletotrichum coccodes were inhibited 100%， 93%， and 94% by 5% boiled water extract of welsh onion root， respectively.
Furthermore， five crop pathogens Pyricularia oryzae， Phytophthora cactorum， Colletotrichum coccodes， Thanatephorus cucumeris， and Botris cinera were inhibited 80-100% by 5% water extract of garlic (cv. Namdo)， but suppression rates in other garlic cultivars were low. Aforementioned five crop pathogens were also inhibited 95-100% by 0.3% allyl disulfide. Higher suppression rates of the above five pathogens may be related to higher thiosulfinate content in garlic. Broadleaf plants such as cucmber， Calystegia sepium and Quamoclit coccinea (L.) Moench， grass plants such as barely， Digitaria ciliaris (Retz.) Koel and Echinochloa oryzoides (Ard.) Fritsch were inhibited higher in water extract of onion (cv. Sunpower) than extracts of other 4 onion cultivars (Sinseonhwang， Deosingihan， Romang and Cheonjujeok). The plants were showed the highest inhibition in boiled water extract of Seosan garlic among 3 cultivars (Namdo， Heanam and Deaseo). In addition， shoot and root lengths of cucumber， barley， and barnyard millet (Echinochloa oryzoides (Ard.) Fritsch) were inhibited 50-100% by 0.5% allyl disulfide. Generally， the order of total phenol and total flavonoid contents， and DPPH radical scavenging activity was onion> garlic> welsh onion. Total phenol， total flavonoid， and allyl disulfide contained in Allium species plants may be related to suppression rates of crop pathogens and weeds. Thus， the plant extracts selected from Allium species can be used for control of crop diseases and weeds in organically cultivated crop fields.