Appears on all new leaves black dust like particule.

how to problem solved

The sooty substance is actually called sooty mold, and it is a fungus that is spread by insects. It is an unattractive nuisance, but in itself it is rarely lethal. I have had success making a solution of soapy water and spraying my plants every few days. I use two big squirts of dish soap to one gallon of water in a one-gallon sprayer. It is important to douse every inch of the plant, paying special attention to the underside of leaves.