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Too many stacked crop trait genes?

When the first transgenic crops came out, the variety numbers and trait designations became a bit of an alphabet soup.

Then it was only one or two traits normally not stacked. Today there are double and triple stack varieties resistant to herbicide and with traits to genetically control insects.

A trio of industry leaders and a Colorado State University weed specialist say new future trait crops will carry even more letters and monikers. That begs the question; how many is enough? Probably six or seven.

Beyond that, it may be genetically impractical, if not economically unfeasible, according to some of the industry’s leaders.

Phil Westra, Colorado State University Extension specialist, questioned, “How do you get a farmer to pay?” for a multitude of traits in one variety and then go to the expense of mixing several herbicides in a spray tank, all in the name of weed control and combating herbicide resistance.

Westra joined Monsanto’s Rick Cole, technology development manager; DuPont’s David Saunders, product development manager; and Bayer CropScience’s Darren Unland, also a product development manager, in detailing what the future may hold for herbicide-resistant crops.

The four also told scientists at the Western Society of Weed Science annual conference in Hawaii that the issue of weed resistance to classes of herbicide will not go away, even with multi-trait varieties. It actually may become more complicated.

It was symbolically appropriate that the discussion of herbicide resistance took place in Hawaii.

For it was in the Aloha State where herbicide resistance was first reported against 2,4-D in 1957. Since then, weed resistance to herbicides has been documented for at least a dozen herbicidal modes of action.

However, it probably never has been a more widely debated subject with the introduction of herbicide crops.

It is such a hot topic, companies find themselves playing catch-up in countering resistance. Scientists say it doesn’t take long for overuse, misuse or total dependence on an herbicide to create resistance. In the dozen years since glyphosate-resistant crops were introduced by Monsanto, about a dozen weeds have been documented as resistant to glyphosate. The list is expected to grow.

There are now 200 million acres of glyphosate-resistant crops in the world. Compounding the resistance issue is that one of the safest and most effective herbicides ever developed is now the cheapest, inviting overuse and resistance buildup.

Asked about his concerns regarding herbicide resistance, Cole said, “I worry more about $5 Roundup.”

Monsanto is developing dicamba-resistant crops to counter glyphosate resistance, especially in controlling Palmer pigweed (Palmer amaranth). Cole said Dicamba-resistant soybeans are expected to be available to growers in 2014.

Later will come dicamba-resistant cotton, as well as corn with tolerance of Dicamba. Also being developed is cotton resistant to glufosinate.

Cole said, however, Monsanto is not abandoning its Roundup Flex technology as it adds new resistant genes. For example, glyphosate-resistance will be combined with the Dicamba and glufosinate traits in cotton.

Cole said several issues evolve with these multi-resistant stacked genes. One is the necessity of multi-modes of action spray tank mixes and cleanout of those tanks.

The resistance issue with identical back-to-back same trait crops was raised in one resistance management study. Rotation to non-trait crops is highly recommended to ward off resistance. Also, the weed scientists are adamant about using pre-plant herbicides in managing against resistance.

DuPont has its GAT trait technology, which is a combination of glyphosate and ALS resistant traits in one package.

Bayer has its LibertyLink resistance package and is working on glufosinate and isoxaflutole resistance biotech crops.

Saunders calls all these valuable tools in controlling weeds. However, he added, there will never be “silver bullets” in weed control. Weed control, however, will become more complex – like what to do with volunteers in rotated herbicide resistant crops.

While companies are moving headlong into the seed trait business, Unland said there is a growing need for new modes of actions to put into the herbicide mix. He says Bayer CropScience is one of only two major agchem companies looking for those new modes.

Even with all the new technology, the issue of weed resistance will not go away, according to Saunders.

“What is going to happen when there are 200 millions acres of Dicamba-resistant crops in the world in 12 years like there are 200 million acres of glyphosate-resistant crops now?” Westra asked.

It was suggested that resistance management be regulated by applications from the label, if resistance is too widespread.

Cole said Monsanto does not favor that. “We prefer to educate rather than to regulate.”

Regardless of what technique is used to battle resistance, it will continue to be an issue as a growing number of crops are introduced with a wide array of resistant traits. “Sure there will be resistance in the future” involving new traits, Saunders said.

Growers will use the cheapest and most efficient weed control techniques available. It is the role of technology providers and chemical companies to “provide the tools for that ... we are planning ahead all the time,” Saunders said.

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TAGS: Management
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