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RR canola evolves into vexing weedRR canola evolves into vexing weed

Harry Cline 1

August 20, 2010

10 Min Read

There is a new glyphosate-resistant weed. It is so new it’s not anyone’s fault.

NORTHERN CALIFORNIA UCCE farm advisors Doug Munier, left, of Glenn County and Kent Brittan of Yolo County are getting out the word about a new Roundup-resistant weed that has popped up in the state.

Cannot blame this one on overuse of Roundup or poor weed resistance management.

It’s a volunteer that in California blindsided farmers and researchers.

It is Roundup Ready canola, a crop that turns into a weed if you are not careful.

Canola shatters badly during harvest. University of California Cooperative Extension farm advisors Doug Munier in Glenn County and Kent Brittan in Yolo County knew that when they became part of team testing RR canola as a possible oil crop for biofuel.

Munier, Brittan and others found yields too low to make canola a profitable irrigated California crop at current prices. They gave up on canola, but canola did not give up on California. It is still around in many fields, three or four years after it was grown as a commercial crop.

Canola shattering losses can potentially be huge.

However, there is far more to it than that.

“What makes canola a different critter is that a significant percentage of this shattered seed does not germinate the following year, which is very different from other California field crops,” Munier explained. “When the shattered seed is incorporated into dry soil, it creates what is called secondary (seed) dormancy.” This is a common genetic trait for canola.

A canola crop that yields 1,400 pounds per acre would produce the equivalent of 182 million seeds per acre or 4,177 seeds per square foot, according to one Canadian researcher. Irrigated California canola has yielded 3,000 pounds per acre. A little shatter goes a long way.

From a 5 to 10 pounds per acre crop seeding rate, Munier said, shatter at harvest can produce up to 10 times the initial seeding rate to fall on the soil to germinate for years to come.

In canola growing areas, the shatter issue has created the axiom, “Once a canola grower, always a canola grower,” because the shattered seeds remain viable and dormant in the soil for years.

Compounding the problem is the fact this secondary dormancy seed may germinate year-round in climates like California.

That can be a nettlesome problem, but it is made far worse when it is herbicide resistant canola.

This became evident in a Sacramento Valley Roundup Ready alfalfa field recently.

“The grower sprayed his Roundup Ready alfalfa and got beautiful weed control except for what he thought was mustard. The herbicide did not touch it. His PCA looked closer and discovered it was Roundup Ready canola. Recognizing the problem, he rogued out the canola,” he said.

With canola’s secondary dormancy, had the grower let the canola go to seed, the problem would only have magnified for years.

In a trial planted by Munier in the Chico area, he planted RR canola in the fall of 2006. Harvested the next summer, the field was summer fallowed in 2007 followed by fall-planted wheat. RR canola volunteers from the 2007 harvest are still sprouting in 2010.

“This is not just a weed, but one totally resistant to Roundup, a herbicide that is intensely used in a wide variety of high value crops in California,” Munier said.

There are 1.5 million acres of canola grown in the U.S., primarily in North Dakota, Minnesota, Oregon and Montana. Canadian farmers have produced canola on up to 15 million acres annually in recent years. Those numbers are expected to grow as both nations search for new sources of biofuel.

As much as 90 percent of the U.S. and Canadian canola crop is grown from biotech seeds, according to Barry Coleman, executive director of the Northern Canola Growers Association and canola grower in North Dakota.

Munier, Brittan and other UC researchers have looked at it as a potential California crop at four locations in the state.

“Roundup Ready canola on roadsides and in crops is not a crisis in California because we have not grown much canola and likely never will. However it is an issue. We rely heavily on Roundup in annual and perennial crops and we are very restricted in the use of phenoxy herbicides, the most common herbicide for Roundup Ready canola control. Munier noted that in the areas where most U.S. canola is grown phenoxy herbicides can be much more freely used to control RR canola than in California. This may make RR canola less problematic.

However, there apparently is plenty of biotech canola on the roadsides. At the Ecological Society of America’s annual meeting researchers reported that 86 percent of 406 canola plants collected from 5,400 kilometers of interstate, state and county roads in North Dakota tested positive for glyphosate or glufosinate herbicide traits. Two samples reflected stacked herbicide resistant traits, even though Canola varieties with multiple transgenic traits have not yet been released commercially.

“With any technology, there can be weaknesses. With Roundup Ready canola, this secondary dormancy is a significant weakness,” Munier said.

Canola is in the mustard family and several mustards are common weeds in fields and roadsides in California. Canola seed is very tiny like other mustards. It is so small it is used in a biblical parable to reflect how much can grow from a tiny seed.

RR CANOLA growing along a roadside.

Munier saw the parable come to life in a few glowing yellow patches along a 100-mile stretch of highway from Chico, Calif., to Davis, Calif. It was the hauling route for a combine used to harvest RR canola plots in both Chico and Davis.

Munier began to feel like Johnny Appleseed when roadside maintenance crews along his 100-mile haul were perplexed to discover patches of what they thought was mustard blooming bright yellow after an application of glyphosate. It wasn’t wild mustard, it was RR canola seed sailing off the borrowed combine.

Another large patch has appeared in the medium of I-505 Interstate near Vacaville, Calif. Brittan surmises it came from a truck hauling canola to a feedlot.

“If you want to determine if a bottom dump trailer will spill canola seed, use water to test it,” laughed Munier. “The seed is so tiny it will almost flow out of a bottom dump like water — I don’t care how tight you think it is.”

Visually differentiating between wild mustard and RR canola is difficult. Canola has a smooth, waxy leaf and stem and a grayish green color. Wild mustard is typically green with no waxy coating.

“I can sometimes tell the difference from my pickup, but others may not,” said Munier.

Monsanto has become involved in the issue, providing test strips that identify genetically modified RR canola. Monsanto has also offered free Monsanto sulfosulfuron herbicide to control the roadside RR canola. It is marketed under the trade name Outrider. It is a selective post-emergent and pre-emergent systemic herbicide used to control annual and perennial grass and broadleaf weeds in non-crop areas.

Another herbicide that works on roadside RR canola is Milestone VM Plus specialty herbicide from Dow AgroSciences, according to Munier.

“Phenoxy herbicides work well, too, but they are limited as to when they can be used,” said Munier. Many counties enforce no-phenoxy periods to protect crops from drift damage.

John Young, Yolo County ag commissioner, took Monsanto up on its offer. His office oversees roadside vegetation management in the county.

Young said controlling roadside weeds migrating from agriculture is not new. Volunteer wheat and oats seeding from passing trucks and farm equipment are common, but not an issue with adjacent farmland.

Roadside sunflowers are an issue. Many acres of sunflowers are grown for seed in the Sacramento Valley. “It is a pollen drift issue,” Young points out, challenging his department to control wild sunflowers.

“When we notice something that should not be in that 8-foot roadside swath, we need to change our management practice, whether it is chemical control or mowing,” said Young. That is what has happened with the introduction of RR canola.

Young said the chemical cornerstone of roadside vegetation management is glyphosate or Roundup. “When you find something that is resistant to Roundup, you just find something else to control that resistant weed. When we noticed the canola on the roadside, we just changed our management practice.”

California Department of Transportation will be using Outsider from Monsanto this season to control the RR canola.

YOUNG, FERAL canola plants adjacent to a field and a blooming almond orchard.

George Gough, Monsanto’s director of Government Affairs for the West, based in Davis, Calif., quickly got involved when the roadside problem became an issue.

“Doug Munier let us know what was happening early on,” Gough said.

“When it became evident Roundup Ready canola on the roadside posed a problem we offered technical input and free herbicide to take care of the problem.”

Brittan said the weed potential of RR canola blindsided him and growers who grew the canola. However, he said growers are aggressively cleaning it up with cultivation and herbicides.

“I have been monitoring those commercial fields where it was grown. I am not concerned with conventional farming. It is being reduced each year. I think farmers can handle it,” he said. However, he is worried about RR canola on roadsides and the impact it could have on adjacent farmland if the feral canola goes to seed and gets into fields of organic mustard seed production from roadsides. Mustard is used as a common ground cover in orchards and vineyards. It could create a perennial weed issue.

Munier and Brittan are concerned growers who have never grown RR canola may think it is mustard. The same is true for vineyards and orchards.

“We have had meetings with growers and others, alerting them to the problem. We want to spread the word so the problem will not get out of hand,” Munier said.

Monsanto has issued a bulletin on how to control volunteer RR canola in fields.

Monsanto research indicates that the addition of 2,4-D (0.23 L/acre of 500g/L amine formulation or 0.16 L/acre of 700 g/L ester formulation) to a Roundup burn-off provides good consistent control of volunteer Roundup Ready Canola prior to seeding a cereal crop. Note that ester formulations of 2,4-D are not allowed in most of California. Follow-up in-crop treatments will be required for later germinating seeds.

Volunteer canola typically germinates and emerges as the soil warms up in the spring in the Northern U.S. and Canada. Munier says it germinates in California mostly in the fall with the first rains or irrigation. “However, I’m seeing it germinate year-round, but at much lower frequency,” he added. Before using any pre-seeding treatments, check the field to see what weeds need to be controlled, and pick the right product or products for the weeds in that field. For producers looking to control volunteer RR canola that has germinated prior to seeding, there are several cost-effective tank mix registrations available.

Monsanto’s recommendations:

• Prior to: Wheat, barley, rye, oats, corn, flax, canary seed, 14 other seedling grasses

Products: Roundup (rate: 0.33 - 0.50 L/ac) and Buctril M (rate: .2 - .4 L/ac)

• Prior to: Wheat, barley, rye, oats, corn (field and sweet), flax

Products: Roundup (rate: 0.33 - 0.50 L/ac) and MCPA Ester 500 (rate: .2 - .4 L/ac)

• Prior to: Wheat, barley, rye, oats, corn (field and sweet), flax, field peas

Products: Roundup (rate: 0.33 - 0.50 L/ac); MCPA Amine 500 (rate: .2 - .28 L/ac)

• Prior to: Wheat, barley, rye

Products: Roundup (rate: 0.33 - 0.50 L/ac); 2,4-D Amine 500 (rate: .22 - .57 L/ac)

• Prior to: Wheat, barley, rye

Products: Roundup (rate: 0.33 - 0.50 L/ac); 2,4-D Ester 600 (rate: .19 - .47 L/ac)

email: [email protected]

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