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Consider Fall Herbicide Applications to Control Tough Weeds

Consider Fall Herbicide Applications to Control Tough Weeds
If fall herbicide applications fit your cropping system, now is a great time to set the stage for better weed control in 2015.

If fall herbicide applications fit your cropping system, now is a great time to set the stage for better weed control in 2015.

"Fall is an ideal time to control marestail," says Dan Childs, technical weed control rep for Monsanto. He spoke to farmers visiting two field days at one of Monsanto's research farms this summer.

"The weakest point in the growth cycle of marestail is generally in the fall," he continues. On plots where he applied Roundup, 2-4D and dicamba last fall, fields were clean this spring. He achieved similar results with 2,4-D and dicamba alone.

Locked and loaded: Jason Holman says that varieties with dicamba tolerance will have good genetic packages once the technology is approved.

There are more options in the fall because you're not worried about plant-back restrictions, Childs notes. One option is Sharpen plus metribuzin. You can also apply First Rate or Classic.

The latter two products won't control ALS-resistant marestail. ALS inhibitor refers to the mode of action by which the herbicide kills weeds. Scientists have developed a numbering system for modes of action so you know you're applying more than one mode of action in all applications combined for the season. It's an important strategy to help prevent further weed resistance. Mode of action for ALS inhibitors is number 2.

Related: Survey Says More Growers Considering Fall Weed Control

Fall control, however, isn't effective against all weeds. Childs notes that Palmer amaranth doesn't respond to applications made during dormant conditions. Consider it resistant to both glyphosate- and ALS-resistant herbicides, Childs adds.

Winter annuals can be controlled in the fall, but make sure herbicides have activity against winter annuals. Some combinations may not deliver the results you want if the field is infested with winter annuals.

Some farmers have more than jokingly referred to winter annuals as their cover crop, and not worried about controlling them. However, Eileen Kladivko, a Purdue University Extension specialist working on soil health, has found winter annuals are actually are poor cover crops. They produce a very small amount of top growth compared to actual cover crops.

If you're into a system involving cover crops, it probably means you won't be applying fall herbicides, at least on those fields.

"We need products like Roundup Xtend to give us better flexibility controlling resistant weeds," Child says. Right now the product, containing dicamba, is tied up in regulatory approvals by the Environmental Protection Agency.

This product can only be applied to Roundup Ready Xtend soybeans with dicamba resistance. Jason Holman, who works on the plant breeding side with Asgrow, says once the trait is approved, several excellent varieties will be available.

If there's an upside to the slow approval process, it's that plant breeders have extra time to select for varieties with the dicamba –tolerant trait, plus other offensive traits, such as phytophthora resistance. Compared to some trait products released perhaps too quickly in days gone by, dicamba-tolerant soybeans should have an excellent genetic package when the system is approved, Holman concludes.

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