Primary date: March 7, 2020
A candidate whom wishes to be on Louisiana's Presidential Preference Primary has to either:
Pay a filing fee of $750 plus a party fee of $375 to the Louisiana Department of State
File a petition to the Secretary of State, with 6,000 signatures, a 1,000 of which come from registered voters "affiliated" with the party from each of the 6 congressional districts.
The first day to collect signatures is August 6, 2019 and the last day to submit the petition is November 6, 2019
Here is the official paperwork on Louisiana's Presidential Preference Primary