"Mike would do anything for any farmer," his wife, Karen, said. "If there was a farmer who got sick in harvest time or planting time or whatever, he would say, 'What can I do to help? Here's my equipment. Here's my guys. Let's go do it.'"

But across much of farm country, a dispute over a common weed killer is turning neighbor against neighbor. The furor surrounding the herbicide known as dicamba has quickly become the biggest controversy of its kind in U.S. agriculture, and it is even suspected as a factor in Wallace's death in October, when he was allegedly shot by a worker from a nearby farm where the chemical had been sprayed.

Concern about the herbicide drifting onto unprotected crops, especially soybeans, has spawned lawsuits and prompted Arkansas and Missouri to impose temporary bans on dicamba. Losses blamed on accidental chemical damage could climb into the tens of millions of dollars, if not higher, and may have a ripple effect on other products that rely on soybeans, including chicken.