I hope you're going for hyperbole here. If not, you may be surprised at the proportion of farmers who do understand how biology works; who do work with vets and other professionals and follow research into animal health and disease.
Your statement does a large number of people a disservice.
What the parent is talking about are the broader consequences of decisions that farmers make based on the limited scope of their expertise.
A big example is the use of antibiotics to manage disease in livestock, which obviously takes some understanding of biology and consultation with vets and other experts. Unfortunately, it is very likely contributing to the evolution of bacteria away from susceptibility to those antibiotics.
Farmers are not unique in the fact that their expertise doesn't cover all possible outcomes. That's true of everyone. It doesn't mean they are ignorant and I don't think it does them a disservice to say it.
What the parent is talking about cultural factors that might lead farmers or other "small town" folks to dismiss the findings of other experts, because those expert don't know as much about farming. A big-city evolutionary biologist Ph.D. is going to look stupid if they're quizzed about raising cattle or shooting guns. That doesn't mean they're wrong about bacterial evolution.
This is not limited to farmers, of course--in big cities you get people who don't listen to doctors about vaccines, simply because they don't know anything about doctors except that they make a lot of money.