Causal Agent: 

Fungus (Oidiopsis sicula)

Characteristic Symptoms:
 
The most common sign of the disease is the white powdery mold/pustules on the underside of the leaves.
   
Pale yellow spots or lesions which later become necrotic at the center may be observed on the upper leaf surface.
   
Defoliation is common when infection is severe, thus fruits usually become susceptible to sunscald.
   
Conditions for Disease Development:
 
The disease occurs in both dry and humid climates.
   
The pathogen has a wide host range.
   
Spores can germinate at any relative humidity when  temperature is cool (15-25°C). 
   
Once infection has occurred, warm days (above 30°C) with cool (below 25°C) and humid nights favour rapid disease development.
   
Spores are carried by wind or rain splash to new hosts.
   
Disease incidence is greater using furrow or drip irrigation than using overhead irrigation. Spore germination is inhibited by water on plant surfaces for extended periods.
   
Management and Control:
 
Use resistant varieties, if available.
   
Provide good air circulation to minimize disease incidence and severity.
   
Avoid excessive use of N fertilizer or use a slow-release fertilizer.
   
Remove weeds that may serve as alternate hosts of the fungus.
   
Avoid furrow irrigation when infection is high.
   
Apply sulfur-based fungicide  (e.g. Kumulus®) or thiophanate-methyl (e.g. Tango, Topsin®) at the early sign of the disease. 
   
When plants are susceptible, apply protectant and curative fungicides such as azoxystrobin (Amistar®, MiradorⓇ, RobatoⓇ), difenoconazole (e.g. ScoreⓇ, MontanaⓇ, PursueⓇ, BashⓇ), tebuconazole (e.g. Folicur®).
   

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