The citations were issued after a commercial vehicle inspection of the country music star's tour bus, state police said in a news release.
"When the door was opened and the trooper began to speak to the driver, he smelled the strong odor of marijuana," the news release said. A search of the bus produced 1 1/2 pounds of marijuana and 0.2 pounds of narcotic mushrooms, according to state police.
Nelson's publicist, Elaine Shock, declined immediate comment.
Also cited were Tony Sizemore, 59, of St. Cloud, Fla.; Bobbie Nelson, 75, of Briarcliff, Texas; Gates Moore, 54, of Austin, Texas; and David Anderson, 50, of Dallas.
Each was released after being issued a citation.
Nelson, 73, has recorded songs including "On the Road Again" and "City of New Orleans."