Root rot of onion caused by Pythium irregulare and Pythium coloratum

Pythium irregulare and Pythium coloratum were isolated consistently from roots of onion plants exhibiting root rot and associated foliar symptoms in fields located in Organe County, NY. P. coloratum predominated following extremely wet weather in 1984 and 1986, while P. irregulare was prevalent following moderately wet weather in 1985. Both species produced root rot symptoms similar to field symptoms when 12 week old onion plants (cv Downing Yellow Globe) were inoculated and incubated in a growth chamber at 14°C for 10 days. This is the first report of P. irregulare and P. coloratum as causes of root rot of onion.