Zoospores follow chemical signals from root exudates, swim to roots and encyst, then infect root cells. Secondary inoculum from zoosporangia can be produced on colonized roots. It is generally accepted that most infection takes place only in very young emerging seedlings. Important factors include susceptiblity. Susceptible varieties with moderat e to high tolerance do not undergo stem rot, but root damage may occur.
Flooding is a critical factor in the disease cycle.
Soil compaction and tight soil texture enhance this effect. Levels of Phytophthora sojae in the soil are increased under no till conditions. These races are controlled the the Rps-1K gene, but emerge nce of race 25 suggests that this source of resistance my be lost in the near future. Control Measures Vertical resistance genes have been widely used . Currently, Race 3 is the most common race.