What impact could a terrorist have on the nation through the use of biological war on our agriculture?

Bioterror attacks on America’s agricultural system are capable of inflicting varying degrees of economic and environmental damage depending on the target and method of the attack.
Consider an attack that destroys a storage facility or deploys a toxic agent over agricultural fields. Such a localized attack would have a serious impact on the affected area and the people, animals, and crops therein, but would be unlikely to impact the larger agricultural system nationwide unless the scale of the attack were enormous.
By contrast, a more systemic attack affecting one or more major components of the food chain would ripple throughout the country. For example, an attack that managed to swiftly kill all or most pollinators would cripple the agricultural system nationwide because most of America's crops rely on pollinators.
The American agricultural system is already under considerable strain due to shifting patterns of precipitation, temperature, disease, and drought as a result of climate change and resource mismanagement. Further, the economics of farming have become increasingly hard, with rates of foreclosures and suicide high among farmers. In this context, attacks that hit already weakened farmers could be truly devastating to both the farmers and those they supply.

Biologically based attacks on agriculture, or food produced from it, is called agro-terrorism. The effects could range from slight to apocalyptic, depending on the severity, scope, and number of attacks. Clearly, multiple attacks on multiple types of targets would compound the damage, but even a select few attacks could create big problems by sowing panic and destroying the public's confidence in food and its suppliers.
If a pathogen were introduced against a targeted crop, the resulting disease or damage might necessitate the destruction of huge amounts of food destined for humans or animals. If animals were infected or ate infected food, they might have to be slaughtered and their bodies safely disposed of. The economic effect on agribusiness, from giant corporations down to family farms, would be severe. Another problematic effect and related target is the water supply, as farm runoff would poison the water. Additionally, as U.S. farmers sell much of their product overseas, international commerce would suffer, and people overseas could also be sickened by tainted food.
The direct interference with crops already harvested is also possible, in storage facilities before processing. If the affected foods and beverages were consumed, resulting epidemic diseases could also overwhelm hospitals and, worst case scenario, the morgues.