Beginner

Scientific Name
Alternaria spp., Pythium spp., Phytophthora spp., Rhizoctonia spp.

Identification

• Seeds infected prior to emergence may rot
• If infected seedlings emerge, they are usually weak and lack vigour
• Post-emergence infections cause the seedlings to rot at soil line
• Other symptoms include mouldy seeds and lesions or cankers on roots, hypocotyl or lower stem

Often Confused With
Insect damage
Environmental damage

Period of Activity
Seeding until 2-4 weeks after transplanting.

Scouting Notes
Transplant growers should monitor emergence and growth. Dig up non-emerged seeds or seedlings and look for symptoms of rotting or stem girdling. Scout fields soon after transplanting to assess the plant stand and its establishment. Look for wilted, stunted, or dead plants. Dig them up and examine for symptoms of rotting, stem girdling, insect feeding, or environmental damage.

Thresholds
None established.

Advanced

Scientific Name
Alternaria spp., Pythium spp., Phytophthora spp., Rhizoctonia spp.

Identification
Seeds infected prior to emergence rot and typically fail to produce a seedling. If the seedlings do emerge, they are usually weak and lack vigour.  Post-emergence infections cause the seedlings to rot at soil line.  This usually occurs within 2-4 weeks of emergence (or transplanting).  Affected plants tend to curl downward or melt into the soil. Other symptoms include moldy seeds and lesions or cankers on the roots, hypocotyl or lower stem.

Often Confused With
Insect damage
Environmental damage

Biology
Alternaria infection of seedlings can cause small stem lesions that can enlarge and eventually girdle the plant.

Pythium and Phytophthora are water-molds.  They are particularly destructive in wet and cool soil conditions. Pythium infection may result in pre- or post emergence damping-off, distinguished by dark-coloured, water-soaked lesions on roots or stem. Seed infected by Pythium becomes soft and water-soaked.

Rhizoctonia solani persists in soil as a hard resting structure (sclerotia) and grows as microscopic threads through the soil. This damping off pathogen tends to prefer slightly warmer and dryer soil than the water molds. Often, Rhizoctonia will girdle the stems of susceptible crops slightly above and below the soil line. Lesions are tan to reddish-brown in colour.

Period of Activity
Seeding until 2-4 weeks after transplanting.

Scouting Notes
Transplant growers should monitor emergence and growth. Dig up non-emerged seeds or seedlings and look for symptoms of rotting or stem girdling. Scout fields soon after transplanting to assess the plant stand and its establishment. Look for wilted, stunted, or dead plants. Dig them up and examine for symptoms of rotting, stem girdling, insect feeding, or environmental damage.

Thresholds
None established.

Management Notes
Ensure transplants are grown in sterilized flats and in sterile soil-less mixture in the greenhouse. Do not over water seedlings and transplants. Before planting into the field, ensure all transplants are healthy, disease-free and vigorous.