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Pre is the word

Agriculture.com Staff 07/14/2009 @ 10:23am

Back in 1978, the title track from the hit movie Grease touted the line "Grease is the word."

Well, flash forward 31 years and change the subject to corn and soybean weed control, and the line would be adapted to "Pre is the word."

That's because preemergence residual herbicides can play a valuable role in weed management systems.

Their benefit was apparent to Mike Owen, Iowa State University Extension weed specialist, as he drove through Iowa in late June and saw many weedy fields.

"Butt ugly is not enough to describe them," he says.

Conversely, there were some good-looking fields with few or no weeds present. The difference? Those fields were treated with a residual preemergence herbicide prior to planting. The weedy fields relied solely upon postemergence herbicide applications.

"There are some (farmers) applying early pres, and more considering them," says Owen. "But are there enough applying them? No."

Just don't kill weeds. Manage them.

"We need more farmers to buy into weed management and not just weed killing," Owen says.

Both preemergence/postemergence and total postemergence weed control strategies kill weeds. On a weed management basis, though, the pre/post split wins. Preemergence herbicides can zap early weed growth that stifles early crop development that ultimately crimps yields. By the time postemergence applications occur, yield damage via early weed growth competing for water, light, and nutrients has already occurred.

So why don't more farmers apply preemergence herbicides?

"Growers want convenience and simplicity," says Owen. "There's a feeling that pres are a needless expense. Growers will say, 'it takes too much time, it's too expensive, it's too wet, or I have to plant.'"

Back in 1978, the title track from the hit movie Grease touted the line "Grease is the word."

Early yield loss is invisible. Yet, it's real.


Owen talks about some of the considerations farmers should keep in mind when deciding what type of preemergence herbicide to use.

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