Causal Agent: 

Fungus (Cercospora brassicae)

Characteristic Symptoms:

Leaf spots appear as angular or circular  pale green to gray or white with brown border

The disease is sometimes called frog-eye leaf spot
Leaf defoliation can be observed in  severe infection
Conditions for Disease Development
Cool temperature and frequent rain are necessary for spore germination and infection.  
The pathogen is can survive in  volunteer crops and weeds and can be spread by water-splashes and wind
Management and Control:
Use of  resistant variety (if available).
Remove infected leaves immediately to prevent spread of the disease.

Avoid overhead irrigation.

Spray with fungicides with such as Azoxystrobin (e.g. Amistar®) or Pyraclostrobin (e.g. Cabrio®).

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