This year, soft red winter wheat has been hit badly by the head scab fungus, which develops when it rains during the crop's key growing period. The can produce vomitoxin, a chemical that is poisonous to humans and livestock when consumed at high levels, reports Reuters.

Head scab, which scientists call fusarium head blight, can hit profits of farmers and grain handlers hard, while raising costs for bread and cereal makers. Previous outbreaks cost the U.S. wheat and barley industry $2.7 billion from 1998 to 2000, then another estimated $4.4 billion in 2011. It is too soon to know the full economic losses for 2014.

In addition, unsellable wheat has been competing for storage space with bumper corn and soybean crops about to arrive in the autumn harvest. Cleaning the wheat reduces vomitoxin levels as it sifts out damaged grain, but it can cost about $1 per bushel for farmers. Wheat currently sells at around $5 per bushel.

"This is the worse I've ever seen it," said Wiechert, owner of Wiechert Seed Inc., which he has operated since 1985. The business is 50 miles southeast of St. Louis, Missouri, near the epicenter of a vomitoxin outbreak.

Head scab shrivels the grain. This reduces test, or average, weights from the harvest, which also cuts profits. This outbreak will hit farm incomes that are already down for the first time in several years, shrinking 27 percent in 2013/14 from a year earlier, according to data from the U.S. Department of Agriculture.

Livestock that consume feed made with scabby wheat can get sick with vomiting and diarrhea. Some will refuse to eat the feed, reducing the amount of weight they gain.

Diseased wheat can be blended with higher quality product to reduce the concentration of the chemical to acceptable levels, but some grain handlers are struggling to find good SRW wheat near at hand.

Farmers whose wheat carries large amounts of the pink-tinged damaged crop face deep discounts at elevators, and some grain will get flat out rejected for purchase.