America’s amber waves of grain aren’t just part of our national self-image; they are big business.  The United States exports over $5 billion in wheat every year.  Throughout the Great Plains states wheat farming and related industries are major employers, with thousands of square miles given over to wheat fields.  An attack on our wheat crop would cause widespread economic hardship in the Midwest, with repercussions that could send the rest of America’s economy into a tailspin.  If the wind and weather were right, it could be accomplished with a few hundred grams of spores. 

The wheat rust infecting a plant in Nebraska probably came from a fungus which grew in Texas or Mexico.  As each spore lands on a host leaf, it produces a circular orange pustule, or “rust spot.”  This rust spot can produce as many as 1,000 spores a day, each of which can be carried by the wind to neighboring fields.  Rust thrives in cool, wet weather; in favorable conditions, infestations which began in the southern U.S. can be found as far north as Manitoba and Saskatchewan.  Flag leaf severity on susceptible varieties may range from 40 to nearly 100 percent (Figure 3).  If severe infection occurs before flowering, yield losses may be as high as 30%.  While most strains of wheat grown today have natural resistance to wheat rust, new rust strains have arisen in the wild; in 2001 Arkansas wheat farmers lost 7% of their crop to these new rust strains.  A deliberate release of particularly virulent spores in Kansas or the Dakotas during a wet March could lead to a massive rust epidemic which spread with the winds and which might not even be noticed for weeks or months.

If that sounds bad, a deliberate release of wheat smut could be even worse.  This too could pass unnoticed until the wheat flowered… only to reveal withered black heads filled with spores instead of grain.  When fed into a thresher, this produce grey-black clouds of infectious spores and a distinctive rotting-fish odor.  (One of the common names for this disease is “Stinking Bunt”).  A little wheat smut reduces the price a farmer can get for his crop; a lot renders his crop useless.  Most wheat farmers in the United States use smut-resistant varieties, but this resistance is no guarantee against the introduction of a new strain.  Iraq prepared wheat smut bombs for use against Iran during their long war, and the U.S. government had over a ton of weaponized wheat smut spores before it officially ended biowarfare research in 1968.   

TCK Smut, originally found in Pakistan, was discovered in the Pacific Northwest in 1972.  Since that time China has banned all imports of wheat grown in the region, fearful of importing this disease to its own vast wheat farms.  For wheat farmers, these quarantines can be worse than the disease.  Unlike many countries, the United States is capable of producing much more food than it can consume.  Without a market for this surplus, prices plummet: farmers soon find themselves unable to sell their crops for a break-even price, never mind a profit.  It might be years – or decades – before these quarantines were lifted.  A rust/smut attack could send thousands of farmers into bankruptcy, even if their crops were not directly affected.