Producers taking advantage of unseasonably warm temperatures to apply an initial round of herbicides could find those applications wearing off well before weeds reach peak growth, says Purdue Extension weed specialist Bill Johnson.
"We normally start our planting operations in the middle of April, but with all the fieldwork being done right now we're running 2-4 weeks ahead of schedule," he says. "That means that we're potentially adding one month onto the growing season. And for producers using what we call reduced or setup herbicide rates, they may find their herbicide programs running out 2-4 weeks early as well."
A setup herbicide treatment is not intended to eliminate weed problems. The reduced rate application deals weeds a blow until they are knocked out with a post-emergence herbicide later in the crop season. A setup rate usually is one-half to two-thirds the amount of a full-rate residual herbicide application.
Most farmers bought herbicide or contracted to have applications made for them months ago, so simply buying more weed-killing products or services might not be an option. But they can adjust how much herbicide they use in their first application to avoid setup rate failure, Johnson says.
"If you're using setup rates with a planned post-emerge treatment, I would strongly consider using full rates instead," he says. "Or, when you make your post-emerge treatment, use some of your residual herbicide with your post-emerge treatment."
For corn and soybeans, Johnson recommended herbicides with multiple modes of action to control both grasses and broadleaf weeds.
"You want products that are pretty robust in what they control," Johnson said.
Additional information about herbicide use and strategies is available on the Purdue Weed Science home page at http://www.ag.purdue.edu/btny/weedscience.