Stem and Root Rot of Soybean

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Stem and Root Rot of Soybean

Phytophthora sojae

Fungus


In a Nutshell

  • infected plants develop characteristic long brown lesions extending from the root to about the middle of the stem.
  • Leaves turn yellow and wilt, eventually dying but not falling off the stem.
  • Compacted soils, prone to waterlogging, and heavy rains favor the disease.

Hosts

Soybean

Symptoms

At early growth stages, the fungus causes either seed decay or damping-off of seedlings after emergence. At later plant development phases, infected plants develop characteristic long brown lesions that extend from the root to the about the middle of the stem. The damage to the internal tissues of the main root and stem cause leaves to turn yellow and wilt, eventually dying but not falling off the stem. The first symptoms generally appear in compacted soils, prone to waterlogging, one or two weeks after heavy rain. The disease can lead to heavy loss in susceptible cultivars.

Trigger

Phytophthora sojae is a soil borne pathogen that can survive on plant debris or on seeds for a number of years, even during cold or freezing periods. It can infect plants through the root throughout the season, when conditions are favorable for its development (high soil moisture and optimum temperature of 25 to 30°C). First symptoms usually appear after episodes of heavy rain. The diseased plants seem to be randomly distributed in the field or it can fallow the pattern of low areas or areas with poor drainage.

Biological Control

No alternative treatment is known to this day against this disease.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Seed treatments with fungicides are the only chemical treatment to control P. sojae. Mefenoxam and metalaxyl can be used as seed treatments. Resistance to these fungicides has been observed in some cases. Soil drenching with copper oxychloride (3g/l of water), often together with a antibiotic (Streptocycline) also work.

Preventive Measures

Buy certified pathogen-free seeds.,Use resistant or tolerant varieties.,Improve the drainage of the soil to avoid water-logged areas.