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Phytophthora Seedling Damping Off and Root Rot
Causal Agent:
Phytophthora sojae
Symptoms and Signs:
Young plants:
- rapid yellowing, followed by wilting
- soft rot
- root collapse
Mature plants:
- reduced vigor
- yellowing of older leaves that progresses upwards
- wilting
- plant death
Disease Cycle:
- Overwinters in soil as oospores.
- Oospores germinate when adequate moisture conditions occur and form sporangia.
- In saturated soil, sporangia release zoospores, an infective, motile spore that will swim towards the soybean root where it will attach and germinate.
- The spore penetrates the root surface and colonizes between soybean root cells, causing reduced water movement to the top of the plant.
- Plants eventually die and oospores are produced on plant debris.
Disease Management:
Host resistance: Make sure to choose varieties that have good levels of resistance to P. sojae.
Soil drainage: P. sojae requires saturated soils to infect, so improving soil drainage is a key strategy to combat this disease.
Seed treatments: When P. sojae is a consistent problem, fungicide seed treatments can be used to reduce damping off. Be sure to use the right chemical to provide the best control.
Fertilizer applications: Avoid over-fertilizing prior to planting. High levels of chloride, nitrate, or salt can increase severity of root rot.