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Herbicide diversity tackles kochia

As the weed works hard to outmanoeuvre chemicals, farmers expand the toolbox

Joe Wurz takes kochia control seriously.

The southern Alberta farmer at the Lathom Hutterite Colony takes all weeds seriously, but a few years ago when he observed some healthy-looking kochia plants standing in a patch of dead kochia on farm fields near Brooks — all had been sprayed with glyphosate — he suspected herbicide tolerance had arrived.

“We weren’t seeing these green kochia plants in every field, but they were in patches in different areas,” says Wurz. While he had already been paying attention to herbicide rotation for several years he paid greater attention to using a diverse program of weed control chemistry in an attempt to keep ahead of the weed that’s becoming notorious for outsmarting herbicides.

(And If you suspect you may have herbicide tolerant kochia on your farm, a researcher at Ag Canada in Lethbridge is offering a free, confidential testing service if you send in weed seed samples. See this related article by researcher Charles Geddes.)

Wurz has developed a three-season weed control program using a wide range of herbicides with different modes of actions, in various label-recommended combinations, making sure there is a three-year rotation in the use of various products.

For pre-seeding burnoff and post-harvest he has glyphosate in the tank, but he also uses a tank mix of different herbicides with different modes of actions to add that one-two-punch to controlling weeds. Recently he has been using Nufarm herbicides pre- and post-season — depending on the product they present Groups 3, 4, 6 and 14 chemistry — while in-crop mostly Corteva (formerly Dow AgroScience) products are applied. And also, when growing canola for example, he follows a rotation of different herbicide-tolerant varieties again to use as much chemistry diversity as possible.

“I always make a point of using at least more than one chemistry group with pre-seeding and post-harvest treatments,” says Wurz. “And I also plan a three-year rotation on different fields with the products I do use. And it appears to be working well, particularly with kochia. We’re not seeing any kochia surviving.”

Pre-seeding treatments

For pre-seeding treatments Wurz tank mixes glyphosate with either Conquer, Goldwing or Blackhawk. If he uses one combination in the spring pre-seeding, he doesn’t use the same combination in the fall. Conquer is a combination of Group 14 (cartfentrazone) and Group 6 (bromoxynil) that’s registered for use ahead of canola. Goldwing and Blackhawk are both Group 14 (pyraflufen-ethyl) and Group 4 (Goldwing is MCPA ester, while Blackhawk includes 2,4-D ester). Goldwing is particularly effective used ahead of peas, cereals, corn and canary seed, while Blackhawk is particularly effective in controlling Group 2 and glyphosate-resistant kochia, cleavers and volunteer canola in cereals and soybeans.

photo: Jason Lindgren

 

With usually about 3,500 to 4,000 acres of pulse crops as well as flax and mustard, Wurz likes to use a tank mix including Valtera and Rival 10G. Valtera is a Group 14 (flumioxazin), a pre-emergent product recommended for late fall application — just before freeze-up — that provides early-season broadleaf weed control in pulses, soybeans and wheat. Rival 10G, is another pre-emergent product, Group 3 (trifluralin), that controls broadleaf and grassy weeds as they germinate. It can be used in most cereal, oilseed and pulse crops as well. Wurz, for example, likes to use the Valtera and Rival applied to stubble in late fall, on fields he will seed to lentils the next spring.

As a pre-seed with flax, Wurz likes to use Authority 480, from FMC Agricultural Solutions, tank mixed with glyphosate. It is a Group 14 (sulfentrazone) product.

“We know it is important to use multiple modes of action and also have a three-year rotation of different chemistry,” says Wurz. “We work closely with our agronomist Katie Cowie for advice.”

Reducing the risk

For controlling and reducing the risk of developing herbicide-tolerant weeds, Boyd Bergstrom, western sales manager with Nufarm says it is important to not only use effective weed control products, but make sure they are applied properly, and also pay attention to cultural practices to reduce the number of weeds (and seeds) to begin with.

“It’s been a particularly bad year (or favourable) year for kochia,” says Bergstrom. “The weed has been a particular challenge in Saskatchewan and other parts of Western Canada. The relatively dry spring and hot dry summer were extremely favourable to kochia so it has really raised awareness in how to deal with the weed particularly since it is so susceptible to developing herbicide resistance.”

Along with selecting an effective product and following a herbicide rotation program, Bergstrom suggests a few points to achieve effective weed control:

  • Proper water volume: The herbicide needs to be applied at the recommended rate and with sufficient water. Targeting an application rate using 10 gallons (Imperial) of water per acre will ensure proper coverage.
  • Slow down: Research has shown operating the field sprayer no faster than 14 miles per hour is important to ensure proper delivery of the herbicide. The slower speed reduces the amount of air turbulence behind the sprayer and also reduces boom swaying both up and down and back and forth. Also equip the sprayer with low-drift, 110-degree sprayer nozzles.
  • Lower the boom height: Ideally, set the boom no higher than 26″, again to optimize coverage. Producers want to make sure the boom doesn’t hit the ground, but at 30″ and 40″ heights, for example, there is more chance for spray drift. Again, the objective of these first three points is to get the proper rate applied and get it down so it reaches the weeds and/or soil as required.
  • Herbicide rotation: Use tank mix herbicides that offer different chemistry and different modes of action for weed control. If you use different modes of action in a herbicide rotation it will prevent, or at least delay the risk of weeds developing resistance.
  • Herbicide layering: Similarly, along with different chemistry, apply weed control measures that control weeds at different stages. For example, use a combination that includes a soil active herbicide that kills weeds as they emerge and a tank mixed foliar product that controls growing weeds.
  • Cultural practices: Since kochia favours alkaline or saline soils where moisture carries salinity to the soil surface, look to plant something like a forage seed mix in these areas in the fall that will use up moisture and also provide competition for kochia. And if your seeding system is set on 12-inch spacing consider a narrower row spacing. Narrower spacing increases seedbed utilization, results in a denser crop, and more crop canopy. More plants in the ground helps to supress weeds and also can help increase crop yields.

“Kochia appears to be very adept at developing herbicide resistance and it is also a very prolific seed producer,” says Bergstrom. “Producers need to use as many tools out the toolbox as they can for effective control.”

About the author

Field Editor

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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