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Beginner

Scientific Name
Didymella bryoniae

Identification

• Circular tan-to-dark-brown lesions develop between healthy green leaf veins
  
• Infected leaves often curl inwards
  
• Stem cankers may produce a gummy brown exudate
  
• Later in the season, gummy stem blight infections cause fruit decay, often accompanied by copious amounts of black spores (known as black rot)
  
• On butternut squash, distinct circular bronze patterns (alligator skin) develop on the surface of infected fruit

Often Confused With
Fusarium wilt
Verticillium wilt

Period of Activity
Infections may occur at any stage of crop development. This disease often occurs in “hot spots” spreading out from a single infected seed or plant.

Scouting Notes
While monitoring for other diseases, take note of any wilted plants.  Record the number and location of the infected plants.  Inspect 10 leaves at each of 20 random locations in the field.  Observe both the older and newer leaf growth.  Divide the number of infected leaves by 200 to determine the percent infection.

Thresholds
None established. Apply fungicides at the first sign of foliar symptoms.

Advanced

Scientific Name
Didymella bryoniae

Gummy stem blight infects the leaves, stem and fruit of all cucurbits.  Foliar infections cause premature defoliation, resulting in lower yields and poor fruit quality.  Under wet fall conditions, these rots may result in significant harvest losses and storage decay

Identification
Symptoms first appear on the leaf margins as circular, brown, necrotic lesions surrounded by a yellow halo.  Infected leaf tissue eventually becomes covered with lesions, while the primary veins remain dark green.

Cankers often develop on stems infected with gummy stem blight.  These cankers may produce small black pycnidia. Under severe infections the cankers will girdle the stem, causing the plant to die.

Gummy stem blight also directly infects the fruit.  On most cucurbits, fruit infections cause black rot.  Water-soaked circular lesions on the fruit surface develop copious sooty, black spores.  On butternut squash the gummy stem blight fungi cause a superficial bronzing on the skin with distinct circular patterns.

Often Confused With
Fusarium wilt
Verticillium wilt

Biology
Gummy stem blight survives on crop residue and in infected seed. It prefers moderate temperatures (20- 25°C, 68- 77°F), high humidity and extended periods of leaf wetness.  It often appears once the crop canopy has closed and air movement is restricted. Intermittent rainfall and/or heavy dews aid spore dispersal, promoting the spread of this disease from plant-to-plant. 

Black rot often penetrates the fruit through small wounds, the flower scar or where the fruit belly has contact with moist soil for an extended period of time.  Infections may also be transmitted directly from an infected vine into the fruit. 

Wet fall conditions promote fruit infection, especially if the mature fruit are left in the field for long periods prior to harvest.

Period of Activity
Infections may occur at any stage of crop development. This disease often occurs in “hot spots” spreading out from a single infected seed or plant.

Scouting Notes
While monitoring for other diseases, take note of any wilted plants.  Record the number and location of the infected plants.  Inspect 10 leaves at each of 20 random locations in the field.  Observe both the older and newer leaf growth.  Divide the number of infected leaves by 200 to determine the percent infection.

Thresholds
None established. Apply fungicides at the first sign of foliar symptoms.

Management Notes

• Follow a 2- 3 year crop rotation and use certified, treated seed. 
  
• Broad spectrum fungicides applied at the first sign of gummy stem blight infection will help reduce this disease.
  
• Remove pumpkins and squash from the field as soon as they are mature. 
  
• Store fruit in a cool, dry location and ensure ample airflow.