Not-so-secret atomic tests: Why the photographic film industry knew (2013)
This article paints it as a dark conspiracy that Kodak was informed but not farmers or the general public. It seems to me that there's a simpler explanation: the dangers of radiation were not well understood at the time, and they probably legitimately thought that e.g. the dangers of malnutrition from disposing of contaminated milk were greater than the dangers posed by the contamination.