Phytophthora root and stem rot
Phytophthora root and stem rot is a complicated soilborne disease of economic concern in soybean production areas of NY. Though it has only been confirmed in a handful of counties in NY, it is likely more widespread. As with most of the soilborne diseases, occurrence depends on favorable conditions, including cool and wet conditions and compacted soils at planting time. The disease is exacerbated by flooding of fields after seeding has occurred.
The pathogen survives long-term in the soil as hardy oospores. These oospores germinate to produce sporangia that release the swimming zoospores which infect the soybean roots or are splashed up into the canopy. Infection of seedlings often results in damping off. Symptoms of infection of older plants include lesions beginning at the soil line and extending up the stem, yellow/chlorotic leaves, wilting, reduced vigor, reduction in root mass and death.
Over 70 races of this pathogen exist, making management with resistant varieties challenging without knowing which races occur in a particular field. However, varieties with partial resistance, which adds some level of protection against all races, are available.
Improving soil drainage, reducing compaction, utilizing seed treatments, genetic resistance, and crop rotation are good tools for managing Phytophthora root and stem rot.