I realize this was asked before, but it remains unanswered. Like the original poster, I first encountered the idea through this post (single page version) by Dr. Sarah Taber. Relevant quote here:
The Central Valley used to be peppered with Japanese family farms. Not anymore. What happened to them? WW2's Japanese internment. Japanese internment was a land grab by white farmers. Full stop. The initial call for Japanese internment came mere hours after the Pearl Harbor bombing, from the Salinas Valley Vegetable Grower-Shipper Association.
The simple answer is yes and no. While those who would economically benefit from internment were not silent about their support for the policy, it would likely be more accurate to say internment was the result of widespread Japanese prejudice rather than a singular group.
For some background, President Roosevelt did not specifically authorize internment, but instead through E.O. 9066 gave wide authority to General DeWitt, the military commander of the Western Defense Command, to "prescribe military areas... from which any and all persons may be excluded, and with respect to which the right of any person to enter, remain in, or leave shall be subject to whatever restrictions the Commander might impose".^1
Having been given such wide authority, General DeWitt was not shy about his feelings towards those who had been interned, and in his Final Report described those of Japanese descent as "subversives" who belonged to an "enemy race" and represented "112,000 potential enemies."^2 His views were not a secret, and Justice Murphy would later quote extensively from the report in his dissent in Korematsu while arguing that the policy was driven by racial animus.^3
Furthermore, internment itself was chosen in part over relocation eastward because of the vocal opposition by interior states. The sitting governor of Wyoming was publicly quoted as saying that if those of Japanese descent were relocated to their state, "there would be Japs hanging from every pine tree". ^4
To conclude, I wouldn't dispute the characterization of White farmers support for internment in California, but internment was ultinately driven by public animus that went far beyond that. This animus went to the highest reaches of military command, and far beyond the local concerns of California Farmers.
^1 Ex.O. 9066 (1944)
^2 Korematsu v. U.S., 323 U.S. 214 (1944)(Murphy, J., diseenting)(quoting Final Report, Japanese Evacuation of the West Coast)
^3 Id.
^4 David Kennedy, Freedom from Fear: American People in Depression and War, 1929-1945 (1999).