Weed resistance is always on a grower's mind, but weed shift might be even more of a problem.

The two biggest causes of weed shift – at least recently – are the switch to conservation tillage and the increasing use of glyphosate.

Direct seeding of cereals eliminates most, if not all, tillage passes, explains Joe Yenish, extension weed specialist with Washington State University. And it requires glyphosate to control weeds. The use of glyphosate is also increasing due to Roundup Ready canola and other Roundup Ready crops and simply because glyphosate is one of the most effective herbicides ever invented.

"Roundup has a broad spectrum, it's inexpensive, and it breaks down quickly in the soil," explains Eric Eriksmoen, a North Dakota State University research agronomist. "It's not hard to see why it's so popular."

To keep it viable, though, growers need to give it a little help, he adds.

First of all, growers should consider rotating away from glyphosate occasionally, he says, either by rotating out of Roundup Ready crops and by switching to other inexpensive, broad-spectrum herbicides like 2,4-D or dicamba where possible.

As for weed shift, the simplest remedy is tank-mixing glyphosate with a herbicide that will pick up the weeds glyphosate misses. For example, he says, fall is an excellent time to control dandelion, field bindweed, and winter annuals like downy brome and tansy mustard.

"By adding 2,4-D to a glyphosate tank-mix, most of these weeds won't be as big of a problem in next year's crop," Eriksmoen says.

For spring and summer glyphosate applications, he recommends adding ET, a herbicide from Nichino America that is especially strong against buckwheat, kochia, field bindweed, lambsquarter, volunteer canola, prickly lettuce, Russian thistle, salsify, and dandelions.

ET received its national registration in 2003, and Eriksmoen did some early work with it. "What I like about ET is it gets the hard-to-control weeds that Roundup misses," he says.

In addition, it can be tank-mixed with 2,4-D and gramoxone, either on their own or in combination with each other or with glyphosate. And at a cost of just a few dollars per acre.

Waring recommends tank-mixing one ounce of ET with the recommended label rate of glyphosate, or with one-half to three-quarters of a pint per acre of 2,4-D.
At that rate, ET costs about $3 per acre, making it the least expensive part of the tankmix, says Mike Waring, Nichino America sales representative.

"You must look at tank-mixing with ET to ensure great weed control, or accept the consequences of increasing populations of tough-to-control weeds in your fields," Waring says.

McMullin, a California writer for Nichino, provides this exclusive report for Western Farmer-Stockman. For more on this story, see page 11 in the July issue of Western Farmer-Stockman.

For more information

Eric Eriksmoen, 701-567-4323, [email protected]  

Don Morishita, University of Idaho, Twin Falls Research and Education Center, P.O. Box 1827, Twin Falls, ID 83303-1827
208-736-3616, [email protected]  

Joe Yenish, P.O. Box 646420, Pullman, WA 99164-6420
509-335-2961, [email protected]  

John Burns, P.O. Box 646420, Pullman, WA 99164-6420
509-335-5831, [email protected]  

Mike Waring, 2907 9th St., NE, Great Falls, MT 59404
406-788-2433, [email protected]