Herbicide-resistant crops have arrived in Idaho--valuable new tools that pose their own new challenges.

Early every growing season, Idaho sugar beet growers try to squeeze three to five herbicide applications into a harrowingly tight time frame. If winds or rain delay spraying while weeds are young and still vulnerable to the chemicals, control is likely to come too little and too late.

The application rate is as dicey as the timing: apply too much of a chemical designed for broadleaf weeds and the beets don't thrive; apply too little and the weeds persist.

Enter Roundup Ready beets, carrying a gene from a bacterium that breaks down Monsanto's broad-spectrum herbicide Roundup. Protected from Roundup damage by this feat of genetic modification, transgenic beets sprayed with Roundup stay green and hearty while every weed around them withers.

Who wouldn't want to hammer weeds with this new tool?

"The technology is so good. It's very good," says Del Traveller, assistant to the vice president of agriculture for the Amalgamated Sugar Co. in Twin Falls.

But Idaho sugar beet growers are unlikely to be planting Roundup Ready crops next year. European activists are pressuring the world's candy makers to keep sugar from genetically modified beets out of their products, and the domino effect is at least temporarily keeping herbicide-resistant beets out of U.S. beet fields.

Geoff Crimmins

Farmer Joe Anderson in Potlatch tries out Roundup Ready canola, available for the first time in Idaho in 1999.

That's not the case for Roundup Ready canola, which weed scientist Donn Thill says was planted in the "high hundreds to low thousands" of northern Idaho acres in 1999. Nor was it the case for herbicide-resistant soybeans, corn, or cottonÑnearly 55 million acres of which were planted in the United States in 1998, including several hundreds of acres of Roundup Ready corn in Idaho's Treasure Valley.

"Herbicide resistance is going to be the next big thing in weed control," says Thill. "This is a technology that is going to be used."

In Potlatch, canola grower Joe Anderson agrees. "I think most growers who have been growing canola for a while feel very comfortable that the herbicide-tolerant varietiesÑas they come outÑwill be a valuable tool in their arsenal," he says.

For the past several years at the University of Idaho, agricultural scientists have been evaluating commercially developed herbicide-resistant wheats, canola, sugar beets, potatoes, and corn. Eventually, they hope to contribute their own herbicide-resistant canolas and wheats.

Critics of herbicide-resistant crops raise two primary concerns:

¥ Targeted weeds that are genetically related to the herbicide-resistant crop could hybridize with it, becoming similarly resistant to weedkillers. Theoretically, if several farmers within pollinating distance each planted varieties resistant to different herbicides, a "superweed" with resistance to multiple herbicides could eventually evolve.

¥ Companies that develop herbicide-resistant crops will foster dependence by growers on both the seed they sell and the herbicides they pair with them.

Where herbicide resistance lies on a continuum between being the next best thing to fire and playing with ecological fire will clearly be debated for decades. But both critics and supporters agree there is nothing fundamentally new about weeds becoming resistant to herbicides. More than 200 species of weeds worldwide have already developed resistance to at least one herbicide simply through natural selection: treat any weed repeatedly with the same herbicide and the few individual plants with natural resistance will survive and eventually dominate. Among Pacific Northwest weeds, that's already the case for kochia, prickly lettuce, Russian thistle, wild oat, Italian ryegrass, yellow starthistle, and Powell amaranth.

Nor is there anything new about breeders deliberately increasing the natural variation within a crop species by treating plant material with mutating chemicals, then screening seedlings for promising new qualities, including herbicide resistance. They've been employing this methodÑcalled "mutation breeding"Ñfor nearly a half century.

What's new is the use of genetic engineering techniques to move resistance-conferring genes from other living things into crops. Scientists point out, however, that hybridization between herbicide-resistant crops and related weeds could occur regardless of how the resistance trait arrived in the crop, whether by traditional breeding, mutation breeding, or genetic engineering.

At the University of Idaho, wheat breeders Bob Zemetra in Moscow and Ed Souza in Aberdeen are using traditional breeding and mutation breeding to develop wheats that resist damage by the environmentally friendly imidazolinone and sulfonylurea herbicides. Souza is aiming for "imi" resistance in his highest-yielding advanced lines of hard white wheats, Zemetra in soft whites Lambert, Brundage, and ID 8752814A.

"Our breeding program has put enormous emphasis on disease resistance and a good, strong emphasis on insect resistance, but our producers are telling us that their biggest problems are weeds," says Souza. "If we were to ignore that, we would not be following the mission of the land-grant university to serve the growers of the state."

At Moscow, Thill says American Cyanamid's imi-resistant Clearfield wheat stands up to applications of the herbicide imazamox that level 95 percent of jointed goatgrass and Italian ryegrass. "Right now, we have no chemical way to control jointed goatgrass in winter wheat," says Thill. "This would provide that opportunity."

The reason jointed goatgrass can't be controlled chemically in wheat is that the two plants are too closely related: half of the weed's chromosomes are nearly identical to wheat chromosomes, and herbicides that control goatgrass also kill wheat.

Scientists suspect the imi-resistance gene currently available in wheat is on one of the chromosomes that jointed goatgrass and wheat have in common. Indeed, when jointed goatgrass pollinated imi-resistant winter wheat in experimental fields at Pullman several years ago, the resulting hybrids proved resistant to imazamox.

According to Zemetra, whose cooperative work with federal and land-grant scientists in Washington confirmed the discovery, the wheat-goatgrass hybrids also produced a tiny percentage of viable seeds. This suggested that, not only could the imi-resistance gene move from wheat to weed, but a second generation of resistant hybrids could potentially arise in the field from seed.

Through mutation breeding, Zemetra's wheat-breeding team may be able to keep what he calls a "potentially low-frequency problem" from occurring entirely. If imi-resistance were created in mutated durum wheats--which have no chromosomes in common with jointed goatgrass--the resistance genes could theoretically be shifted into bread wheats on the unshared chromosomes. That would greatly reduce the threat of herbicide resistance transferring to related weeds through unintended cross-breeding in the field.

Canola breeder Jack Brown advocates applying steering, not brakes, to the technology of herbicide-resistant crops--even those crops developed through genetic engineering. "We cannot stifle technology," Brown says--although, like driving automobiles, it carries risk. "Why we continue to do this research is not to tell people to stop driving automobiles but to tell them how to drive automobiles safely."

University scientists also do the research to ensure that growers in Idaho can go head-to-head with growers in other states and nations as herbicide-resistant crops advance in production and acceptance. Regardless of how impressively it resists chemical damage, a variety is "an absolute dog unless it's adapted to the environment in which it is growing," says Brown.

Brown is selecting from among his Idaho-adapted canola lines those showing the most natural resistance to the broadleaf weedkiller Pursuit. Broadleaf weeds can steal 30 to 40 percent of canola production, taint canola oil, and prompt rejection of canola meal. While awaiting the promised "harmonization" that would allow U.S. canola growers to apply all of the herbicides now used in Canada, Idaho growers have just one effective broadleaf weedkiller at hand.

Not only would Pursuit resistance permit broadleaf weed control in Idaho canola fields, it would allow canola to be grown after pea and lentil crops that were treated with the chemical. "If canola acreage is going to expand in the Palouse and Camas Prairie region, it's probably going to have to be imi-resistant because so much of the land has had Pursuit applied to peas and lentils," says Joe Anderson.

Roundup resistance, which Brown hopes to transfer to fall-planted canola lines, would allow northern Idaho growers to follow spring cereals with winter canola. "That option is not available to Idaho growers now," says Brown, "and that really does limit canola production in this area."

Still, Brown doesn't minimize the risk of herbicide resistance in weeds: his research has demonstrated that transgenic glufosinate-resistant, or Liberty Link, canola can crossbreed with weedy mustards, moving the gene for herbicide resistance with it. European scientists have shown that canola pollen can travel up to 2 miles.

"Without any shadow of a doubt, herbicide resistance will cross to weeds," Brown says. "But the impacts of those weeds on our farming systems will be dependent on how we farm. Farmers are going to have to be much more aware of the crops that they grow and the ones that their neighbors grow. They are going to have to be much more careful."

Most weed seeds lie dormant between one and 10 years, Thill says--but individual seeds can last much longer. That's why growers have always wanted to keep herbicide-resistant weeds out of their cropping systems. Prior to the introduction of herbicide-resistant crops, preventing herbicide-resistant weeds depended on the basics of integrated management, among them, avoiding year-after-year use of herbicides that kill in the same ways, rotating with crops that are treated with different herbicides, and cultivating to eliminate surviving weeds.

Now, in rotations with herbicide-resistant crops, growers will need to keep their borders squeaky-clean of potentially cross-pollinating weeds and their harvested fields meticulously free of herbicide-resistant crop seed and volunteers. Grain growers, accustomed to losing seed at harvest as it bounces or blows out of trucks, will need to cover that seed tightly.

University of Idaho crop breeders and weed scientists have committed themselves to extensive and intensive grower education on managing the risks associated with the new technology. In addition, they are developing long-term research to track herbicide-resistant crops through lengthy crop rotations and to evaluate their effects on weed populations in different crop sequences.

According to Thill, researchers at North Carolina State University are learning that it takes just four to five years of steady Roundup Ready or Liberty Link crops to prompt shifts in weed species to those that are not susceptible to those chemicals.

"In the next three to four years, growers in Idaho will have the potential to grow all herbicide-resistant crops," he says. "They'll need to make sure that they not only rotate their herbicides but that they rotate crops depending on the herbicides they will use in each one."

They won't be able to follow one crop with another if both crops are resistant to the same herbicide. Instead, they will need to plug in the right non-resistant crop or a variety that is resistant to a different herbicide.

"We will have to be very careful that we don't overuse this technology and that we use it simply as a tool in part of the system," he says.

In Twin Falls, weed scientist Charlotte Eberlein wonders whether the eventual availability of numerous herbicide-resistant crops will tempt some growers to "get complacent" about their weed control. Noting that many Idaho producers use Roundup before planting or after harvest to "clean up" problem weeds, she warns: "If we select for Roundup resistance in several different weed species, we have lost Roundup as a tool."

Extension weed scientist Don Morishita, also at Twin Falls, shares her concerns. "If the number of Roundup Ready and Liberty Link crops continues to expand, I'm not very optimistic that resistant weeds can be prevented," he says. "I think it's possible--but it will require as much or more management than is currently being used to control weeds."

Producers of direct-seeded small grains, who no longer till their fields, depend on Roundup to destroy competing species before planting and say they couldn't bring in a crop without it. For them, growing Roundup Ready crops--and applying Roundup to them--would be begging for selection of Roundup Ready weeds.

"How will you control volunteers without tillage?" asks Thill. "If you use Roundup in the crop, surely you shouldn't use it before planting or after harvest. You would have to add another herbicide in the mixture to take care of volunteers--and conceivably use more herbicide in the process."

"The long-term implications of herbicide-resistant crops have not been worked out," says Thill. "We don't know the answers, and that's why we need to study these longer term crop rotations."

"It is going to be a relatively expensive technology, so it's probably something growers will want to use only on an intermittent basis," says Souza. "What excites us as scientists is the possibility of actually using this technology well and doing it right."

More than one way to make an herbicide-resistant crop

Crop breeders introduce herbicide resistance in one of two general ways: by inserting a foreign gene (genetic engineering) or by modifying the crop's own DNA (mutation breeding). In both cases, they then use traditional breeding techniques to move the trait into crop varieties adapted to local environments.

Genetic Engineering

Take a gene for a desired trait from an unrelated species (plant, animal, bacterium, or virus) and introduce it into a crop. The resulting genetically modified crop is sometimes called a "GMO," or genetically modified organism.

Example: Roundup Ready crops contain a gene from a bacterium that breaks down the herbicide Roundup.

There are two common methods for introducing foreign genes into crop plant DNA:

1. The gene gun shoots microscopic gold particles coated with genetic material into plant cells. The particles penetrate the cells, and some genes enter the cell nuclei and become part of the cell's genetic material. This applies primarily to narrow-leaved plants such as grasses and grains.

2. Researchers place the foreign gene into the bacterium Agrobacterium tumefaciens then infect the plant with it. The bacterium transfers the gene into the plant's cells, where it becomes part of the cells' genetic material. This works for broad-leaved plants such as tobacco, tomato, and potato.

Mutation Breeding

Treat seeds or plant tissue with chemicals or radiation to modify (mutate) the plant's own DNA. Then grow the seeds into plants, and screen the plants for new qualities.

Example: Imidazolinone-resistant wheat contains a gene that prevents the herbicide from binding to its target site.

Seeds are agitated in a beaker with the mutating chemical. The chemical modifies certain bases in the DNA molecule, resulting in gene mutations.