Wheat is the third most cultivated grain on the planet, behind corn and rice. In 2007, we grew 607 million tons of it and turned it into all kinds of food products — bread, cakes, cookies, cereal, pasta, and even beer and vodka. It's also the target of the fungus Puccinia triticina, better known as wheat leaf rust. This fungal disease kills off affected leaves and causes the grain to shrivel up. A new strain called Ug99 was discovered in eastern Africa a few years ago and it has been wrecking havoc on wheat crops in Uganda, Kenya and Ethiopia. Wheat rust spores travel with the wind, so it's not inconceivable that Ug99 could spread far beyond Africa and make the jump to Asia and North America.