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Glyphosate price spikes recast merits of soybean herbicide split strategy

If higher costs have stopped you from examining other soybean herbicide options to slow glyphosate resistance, take a closer look.

Higher glyphosate costs are closing the price gap between the double postemergence glyphosate treatment and a preemergence/postemergence glyphosate treatment in soybeans, says Kevin Bradley, University of Missouri Extension weed scientist.

A perk for the preemergence/postemergence split is that another mode of action can forestall resistance to glyphosate. It's similar to the fastball pitcher who strikes out a batter with a curveball when he’s expecting a fastball. Likewise, including another mode of action can kill weeds that are expecting another dose of glyphosate.

The residual activity of a preemergence herbicide is another perk.

"We have a fair number of herbicides that have excellent activity when applied preemergence in soybeans," says Bradley.

Up until last year, though, the cost of two postemergence passes of glyphosate was much less expensive than a preemergence/postemergence glyphosate split and couldn't be beat, Bradley says.

That's changing.

"The price of glyphosate is going up, so the economics of applying a preemergence herbicide is becoming more justifiable," says Bradley. "The reason two passes of glyphosate has been so popular in the past is you could put on glyphosate for $5 to $10 per acre for each application. You were looking at a total chemical cost of $20 per acre at the most." Farmers could often pay less if they had had minimal weed pressure.

In comparison, chemical costs for a preemergence chemical and a later glyphosate postemergence application tallied at least several dollars per acre more, to as much as $20 to $25 more per acre.

However, rising glyphosate prices are evening the cost of the two programs, says Bradley.

Generic glyphosate prices recently increased $12 per gallon, and brand name Roundup last week increased in price by 30%, says Lori Hoag, Monsanto spokesperson.

Bradley says one of the most inexpensive preemergence options is Valor, which hovers around $8.50 to $9.50 per acre. Other excellent options include the Authority products that came out in 2007 and 2008, along with Dual, Prefix and Boundary. These treatments run a bit higher, at $10.50 to $11.50 per acre.

"All of these programs will give you excellent control of waterhemp," says Bradley.

That's particularly important in areas like Missouri, where a 2007 survey of agricultural retailers stated four percent of Missouri soybean acres have glyphosate-resistant waterhemp.

"There are a lot of preemergence soybean herbicides that will work," says Bradley. "We've showed, as other people have showed, there's a way to proactively manage glyphosate-resistant waterhemp."

One drawback, though, is that preemergence chemicals can fail to activate if no rainfall occurs within several weeks of application.

If higher costs have stopped you from examining other soybean herbicide options to slow glyphosate resistance, take a closer look.

A particular concern to continued reliance on glyphosate is the tendency of Missouri farmers to plant continuous soybeans.

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