Sierra Sue is a 1941 American western film directed by William Morgan and starring Gene Autry, Smiley Burnette, and Fay McKenzie.

Written by Earl Felton and Julian Zimet, the film is about a government inspector investigating a poisonous weed that is destroying the rangeland supporting the area's cattle.

[1] In Sierra City, George Larrabee (Robert Homans), the president of the Western Stockman's Association, orders the ranchers of the area to burn their land in response to a poisonous "devil weed" that threatens to overgrow the rangeland and kill the cattle.

The local bank president Stacy Bromfield (Frank M. Thomas), a long-time supporter of the ranchers, believes the burning has failed to control the epidemic.

At a meeting with Larrabee and the ranchers, Bromfield announces that he contacted the Department of Agriculture and requested a weed control specialist be assigned to investigate.

Later, Gene and his sidekick Frog Millhouse (Smiley Burnette) rescue a wounded pilot from a crashed plane—a plane carrying a large loan to Bromfield for the ranchers.

After his investigation, Gene attends a meeting with the ranchers and tells them that burning will not work—that in fact it will only cause regrowth—and that the only way to get rid of the "devil weed" is through chemical spraying.