Please read this article, Stahlbush Overtime Dispute, and note that agricultural workers are generally not entitled to overtime pay in Oregon--one of several exemptions that agriculture gets from typical employment law regulations

The workers in the Stahlbush situation were entitled to the overtime pay because they were not actually considered "agricultural workers". The summary says that the employees included in the agreement were those who worked in the food processing division of Stahlbush's operation rather than those who might have worked in conventional farming roles. They were not paid overtime in the first place because the defendant had considered them agricultural workers and those types of workers are not required to receive overtime pay.

I couldn't find an entirely satisfactory answer as to why agricultural work doesn't require overtime while other sectors do. Our vice president-elect was actually recently involved in an act to change this for farmworkers in California because many people don't think it's fair. However, my best guess is that farm work doesn't require overtime because, during the harvest season, there is so much work to be done that overtime hours are a norm. It would be highly taxing on farms to have to pay overtime during harvest peaks for all employees.