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John Ford treated Dorris Bowdon (Rosasharn) quite badly. It may have been because she was the girlfriend of screenwriter Nunnally Johnson and was given the part by Darryl F. Zanuck, or it may simply have been one of Ford's frequent inexplicable dislikes, but he hounded the young actress on every point, from coming on the set with her hair improperly done to taking time to have her hair fixed. Shortly before filming the scene of the dance at the government camp, Jane Darwell expressed her nervousness to Bowdon about "being such a fat old lady and I have to dance and say lines at the same time." When Darwell did the entire take perfectly, Bowdon spontaneously broke into applause, launching a tirade from Ford that made her run from the set crying. The next shooting day, Ford rather awkwardly cheered her up with a little bawdy humor, and the two got on well after that, although she later said, "I was glad I never had to work with him again." Yet, Bowdon in later life also expressed the duality of feelings actors often had for the difficult director when she related a story about how he painstakingly talked her through a very emotional moment that she ended up nailing in a single take. "He was a superb director," she said. "I never saw another director work in a way that was as skilled."
Prior to filming, producer Darryl F. Zanuck sent undercover investigators out to the migrant camps to see if John Steinbeck had exaggerated about the squalor and unfair treatment meted out there. He was horrified to discover that Steinbeck had actually downplayed what went on in the camps.
John Steinbeck loved the movie and said that Henry Fonda as Tom Joad made him "believe my own words".
John Ford banned all makeup and perfume from the set on the grounds that it was not in keeping with the tone of the picture.
John Steinbeck was particularly enamored with the performance of Henry Fonda as Tom Joad, feeling that he perfectly encapsulated everything he wanted to convey with this character. The two became good friends. Indeed Fonda did a reading at Steinbeck's funeral.
While filming the Joads' car traveling down the highway, John Ford wanted to add a shot showing the large number of caravans heading west, so the film's business manager stopped actual cars making the trek and paid the drivers five dollars to escort the Joads' jalopy for the cameras.