Causal Agent: 

Fungus (Alternaria alternata f. sp. cucurbitae)

Characteristic Symptoms:
 

Lesions begin as tiny, tan or brown spots that may appear water-soaked on the underside of leaves.
   
Spots darken with age and appear as round, brown and with concentric rings. Sometimes, these spots may be surrounded by a halo of yellow tissue.
   
Alternaria infections occur only on leaves.
   
Conditions for Disease Development
 
The disease is spread by infested soil, by wind, by irrigation water and by seed.
   
The optimum temperature for disease development is 26˙C.
   
Management and Control:
 
Maintain good field sanitation (e.g. remove & burn affected plant/plant parts).
   
Rotate with non-host crops for 2-4 years to reduce the amount of inoculum.
   
Apply fungicides such as copper-containing compounds (e.g. Champion®, Kocide®, Nordox®) or pyraclostrobin+dimetomorph (e.g. Cabrio to Cabrio TeamⓇ)
   

References:

https://www.extension.purdue.edu/extmedia/bp/bp-44.html

Compendium of Cucurbit Diseases (2010) by The American Phytopathological Society

To view other diseases,  click here.

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