Question: asking about the black spot of citrus 
Answer: suggestion=
apply saaf @ 2gm / l of water , 3 spray at 5 days interval or apply bordeux mixture , 3 spray at 5 day sinterval.
method of prepartion= 100gm lime + 100gm copper sulphate , mix with 5 l of water for each . spray it tothe whole plant body.