All soil-applied residual herbicides have the same Achilles heel, Hager says: they have to be dissolved in the soil through mechanical incorporation or a rain within seven to 10 days.

“We dig everything in,” says Craig Herickhoff. “Yes, it’s a hassle in the spring, but if you don’t get a timely rain, it’s a lot better to have it incorporated.” In 2012, though, seedbeds were dry and cloddy, so he set the planter’s row cleaners deeper than usual. That affected pre placement. “It was perfectly clean between the rows, but in the rows, there was more weed pressure. I think it was because we went deep with the row cleaners, and when we pushed the dirt aside, we pushed some of the herbicide aside, too.”

If incorporation isn’t an option, “you can try to hedge rainfall risk by putting the herbicide out a little sooner,” Hager says. In 2012, though, many parts of the Corn Belt did not receive enough rainfall to move the pre into the soil solution, so weed control suffered.

Nevertheless, “I still believe it was beneficial,” Missouri’s Bradley says. “Our own evaluations showed us there was still some residual weed control, just shorter than normal.” Weed suppression “probably lasted two weeks, where typically it would be about twice as long.”

If it stays dry into 2013, should growers apply a pre-plant herbicide next spring? Yes, Gunsolus says. “We can’t predict the weather. The bottom line is, it’s a risk management tool.”