You are very perceptive and food security is an important issue. Not only from natural diseases and pests, but human population growth, distribution, space, resource availability (water is a big one) and climate change. Crops and livestock are also good potential targets for biological weapons.Thinking about how we treat ourselves and each other during a pandemic, has me realizing oh my god how are we going to treat our crops if anything happens to them? A crop epidemic will be ugly. And America has proven it doesn't get, understand, or comprehend the basics of infections, and as per the norm has shown a reluctance to learn.
Fortunately, many farmers are much more educated in agricultural science and practices than the general public they feed. Also ag companies think about these things. Still, it is a potentially devastating possibility with severe repercussions and no magic bullets.