Service of any paper under this part must be on the attorney or agent of the party if there be such, or on the party if there is no attorney or agent, and may be made in any of the following ways:

(a) By mailing a copy of the paper to the person served by certified mail, with the date of the return receipt controlling the date of service;

(b) By leaving a copy at the usual place of business of the person served with someone in his or her employ;

(c) When the person served has no usual place of business, by leaving a copy at his or her home with a member of the family over 14 years of age and of discretion; and

(d) Whenever it shall be found by the Commissioner or Secretary that none of the above modes of serving the paper is practicable, service may be by notice, published once on the Plant Variety Protection Office website (https://www.ams.usda.gov/PVPO).