Think of somthing on the order or Hoof& Mouth disease, but geneticaly modified to be much more contagious and difficult to treat or vaccinate against. The same would be possible with field crops, and a simple pickup driving down country roads in the middle of the night could spread the diseases. It wouldn't be nescessary to infect entire fields to cause severe damage to the agriculture of a country. What, for instance, would be the effect on farming in your area if a new and highly virulent plant disease were to be discovered in, say, 10% of the crops in your area? A disease so virulent that it simply could not be allowed to spread no matter what the cost to agriculture? It would be like a city being quarantined because an intensly contagious strain of smallpox appeared in several thousand of it's million inhabitants. The economic damage could be done by the quarantining of the area and destroying of crops much more than the disease itself.
I'm not sure what it's like for farmers in your area, but the farmers I know locally could not financially survive any long term disruption of their business. None of the farmers I know have mentioned any extra security measures in their business.