Causal Agent: 

Fungus (Cercospora citrullina)

Characteristic Symptoms:
 
Leaves and fruits can be affected particularly in hot humid conditions.
   
Leaf spots begin as small, round, brown lesions and often with white/light brown center.
   
Sometimes, spots are surrounded by a distinct yellow halo.
   
Under warm and wet conditions, the lesions expand and the leaves may appear blighted.
   
Conditions for Disease Development:
 
The disease is common in humid tropic and subtropical regions.
   
The pathogen survives between crops on crop debris and weeds of the cucurbit family.
   
Conidia/spores are air-borne and are disseminated by wind, rain splashes, tools/implements and field workers.
   
Infection requires free water and is favoured by temperatures between 26-32°C, in which the disease develops rapidly with new infections occurring every 7-10 days.
   
Management and Control:
 
Good field sanitation (i.e., remove and destroy infected plants/plant parts and cucurbit weed hosts) can help eliminate inoculum sources in the field.
   
Crop rotation with non-cucurbit crops for 2-3 years will ensure elimination of inoculum in crop residues.
   
A regular fungicide spray program of copper-based fungicides (e.g. Cupravit®, Super BlueⓇ, Vitigran blueⓇ, FunguranⓇ, KocideⓇ, Hydroxide superⓇ) and  chlorothalonil (e.g. Daconil®, Agronil®, Yoda®, Rover®, Yoda 500Ⓡ) may help reduce incidence and severity especially when crops are susceptible and conditions are favorable for disease development.
   
Use resistant varieties, if available.
   
References:
Compendium of Cucurbit Diseases (1996) by the American Phytopathological Society
   

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