Subject: How do we distinguish viral diseases in plants from deficiency diseases?

Many of the symptoms of viral diseases are identical to that of deficiency 
diseases such as chlorosis,necrosis etc.So how do we distinguish between the 
two so that the plant may be treated accordingly.If a viral disease is 
mistaken to be a deficiency disease and if only additional nutrients are 
supplied and no other precaution is taken against the virus it could result in 
a spread of infection,resulting in crop damage and loss to the farmer.So is 
there any particular difference in the symptoms(chlorosis & necrosis to be 
specific) caused due to the two agents of diseases?
Thankyou for having spent your valuable time in answering my question.Have a 
nice day.

Re: How do we distinguish viral diseases in plants from deficiency diseases?