They are both OK, but crop (singular) can mean both one individually harvested food from one farm, or the collective harvest of a certain kind of food from a region. Crops (plural) could also indicate that there were several different varieties of rice being harvested, therefore the various crops could be damaged.
So both are OK depending upon what you intend to convey. And I would say that in normal conversation you would likely hear both being said, with the speaker not paying particular attention to the subtleties of the plural vs. the singular.