Causal Agent: 

Fungus (Oidium sp.)

 

Characteristic Symptoms:
 
Tiny, light yellow spots on leaf surface.
   
White, powdery growth (mycelia & spores) appears on the underside & upper surface of the leaf as the spots enlarge.
   
Fruit infection has not been observed in the Philippines but has been reported in other papaya growing areas.
   
Conditions for Disease Development:
 
The disease develops quickly under favorable conditions (dense plant growth and low light intensity).
   
High relative humidity is favourable for infection and conidia survival; however infection can occur at RH below 50%.
   
The optimum temperature for disease development is 20-27°C; Under field conditions, the disease stops at high temperatures (38°C and above).
   
The time between infection and symptom appearance is 3-7 days, in which large number of spores/conidia are produced.
   
Management and Control:
 
Maintain good field sanitation (i.e. remove infected plants/plant parts as soon as symptoms are observed).
   
Avoid excessive use of nitrogenous fertilizer.
   
Increase light intensity/avoid dense planting or overcrowding.
   
Spray with chemical fungicides like sulfur-based fungicide  (e.g. Kumulus®) or thiophanate-methyl (e.g. Tango, Topsin®), azoxystrobin (Amistar®, MiradorⓇ, RobatoⓇ), difenoconazole (e.g. ScoreⓇ, MontanaⓇ, PursueⓇ, BashⓇ) and tebuconazole (e.g. Folicur®).
   

To view other diseases,  click here.

Need more help?  Ask the Doctor.