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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: 

  1. Overwinters in soil as oospores.
  2. Oospores germinate when adequate moisture conditions occur and form sporangia.
  3. In saturated soil, sporangia release zoospores, an infective, motile spore that will swim towards the soybean root where it will attach and germinate.
  4. The spore penetrates the root surface and colonizes between soybean root cells, causing reduced water movement to the top of the plant.
  5. 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.