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Ministry of Agriculture, Food and Rural Affairs

Damping-off and Root Rots

Damping off Damping-off and Root Rots Damping off lesions on hypocotyl
Click to enlarge.

Beginner

Scientific Names
Pythium sp., Phytophthora sp. and Fusarium sp.

Identification

  • Seedlings rot at ground level and topple over
  • Seed decay
  • Rotting roots
  • Cankers on lower petioles

Often Confused With
Seedcorn maggot
Wireworm

Period of Activity
Plants are usually infected by damping-off during the seedling stage.  Cool, wet springs and conditions conducive to slow emergence and early development are particularly problematic.

Root rots generally occur during periods of warm, wet weather and may affect the plant at any stage of development.

Scouting Notes
While walking fields, look for wilted plants and/or gaps in the plant stand where the seedlings have failed to emerge.  Dig around the seed trench to look for the cause of the damage.  Record the percentage of the field impacted by damping-off or root rots damage.

Thresholds
None established.

Advanced

Scientific Names
Pythium sp., Phytophthora sp. and Fusarium sp.

Several species of fungi cause damping-off and root rots in cucurbits; including Pythium, Phytophthora, and Fusarium.  While lab diagnosis may help to isolate a specific type of fungi, infected plants are often host to several of these pathogens.

Identification
Seed decay results in poor or uneven emergence.  Infected seeds become mushy and fungal mycelium may be visible on the seed coat.

Damping-off usually infects young seedlings at the soil line.  The hypocotyl and/or crown soften, and the transport of water and nutrients to the growing point becomes limited.  Older plants often exhibit chlorosis on the cotyledons and on the first true leaves prior to wilting.  Plants usually wilt and die within 2- 4 days after the initial infection. 

Look for yellowing, wilted or stunted plants.  Infected plants often have small sunken lesions on the crown or secondary roots.  Unlike many foliar diseases, such as bacterial wilt, root rots will start at the crown and move outwards to the runner tips. 

Pythium infected plants may develop white cottony mycelium on the hypocotyl or the seed coat.  Fusarium infections often produce reddish-brown to pink root or crown lesions.

Often Confused With
Seedcorn maggot
Wireworm

Biology
Pythium infections are most common in cool, wet conditions.  These fungi are present in most soils, and are able to infect a wide range of crops.  Pythium oospores are able to survive in dry soils for long periods of time, becoming active when the appropriate environmental conditions exist.   Pythium also produces zoospores which are able to “swim” to the root surface, rapidly colonizing young feeder roots.

Fusarium is also long-lived and it persists in most soil types, particularly coarse, sandy loams.  Infections often become apparent when a prolonged dry-spell is broken with a heavy rainfall.  Fusarium may occur at any stage of plant growth, although early infections are often the most serious.


Period of Activity
Plants are usually infected by damping-off during the seedling stage.  Cool, wet springs and conditions conducive to slow emergence and early development are particularly problematic.

Root rots generally occur during periods of warm, wet weather and may affect the plant at any stage of development.

Scouting Notes
While walking fields, look for wilted plants and/or gaps in the plant stand where the seedlings have failed to emerge.  Dig around the base of the plant to look for the cause of the damage. 

Record the percentage of the field impacted by damping-off or root rots.  Assess the surviving plant population by counting the number of plants in 10 m (33 ft.) of row.

Thresholds
None established.

Management Notes

  • Sterilize flats and use only sterile soil-less mix for growing transplants.
  • Use fungicide-treated seed and plant only when soil and weather conditions are favourable for vigorous crop development. 
  • Most cucurbits require a minimum soil temperature of 15°C (59°F) for rapid germination. 
  • Ensure healthy and rapid root growth by following a balanced fertility program and maintaining a soil pH of 6.0- 6.5.