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Phytophthora root and stem rot


© Iowa State University

Pathogen(s) causing disease:

Phytophthora sojae

Symptoms:

Young plants show rapid yellowing and wilting accompanied by a soft rot and collapse of the root. More mature plants show reduced vigor and show a general yellowing of the lower leaves that progresses upward, followed by wilting and death. The root system is usually severely affected such that lateral and branch roots are almost completely discolored. Tap roots show a brown discoloration on the surface and, if split, the inner tissues show a tan to brown discoloration.

Conditions:

Conditions favorable for infection occur most often on heavy clay soils with poor drainage. Phytophthora can attack plants at soil temperatures above 50 degrees F, but severe disease generally occurs when soil temperatures are 60 degrees F or above.

Management:

Choosing the right variety with genetic resistance is extremely important. Improve soil drainage so that flooding is eliminated or minimized. Use cultural practices that reduce soil compaction and improve drainage. Improving drainage is particularly important in no-till soils that retain moisture and require less precipitation to saturate the soil. Fungicide seed treatments, like Allegiance or Apron XL, can be used to reduce the early season damping off (higher rates recommended). Allegiance or Apron in combination with genetic resistance provides one of the best options for limiting losses from this disease.

Sources:

Ohio State
ISU

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