The 1940s saw a decline in films about marijuana. With America now at war, the focus was firmly on portraying Americans as happy warriors engaged in a noble mission - no one wanted to dwell on domestic problems such as drug use. There was also a practical issue, as Japanese sources of rope began to dwindle, growing domestic hemp became a patriotic activity; especially after 1942 when the U.S. government introduced its 'Hemp For Victory' campaign, releasing films that showed farmers wading through fields of hemp. Such footage naturally took the edge off the marijuana paranoia.
The exploitation industry however, was reluctant to abandon a theme that had proved so profitable and Devil's Harvest gave the marijuana flick a new and topical twist by attributing America's drug problems to the Nazis.