Now that genetically modified crops cover tens of millions of acres, are super weeds next?
What are the odds that those herbicide-resistant seeds you bought will grow into weeds? Could traits, so valued in crops, spread to weeds and wreak havoc in your fields? Could insects become resistant to your Bt corn? These are a few of the many questions growers, academicians, environmentalists and industry leaders are asking about transgenic crops.
The "odds" depend on a variety of factors, including crop type and the presence of relatives. The amount and quality of risk assessment and testing, and farm management practices also are involved.
Wild and weedy relatives. Corn and soybean growers can probably breathe a sigh of relief when it comes to weed-resistance issues. According to the USDA Animal and Plant Health Inspection Service (APHIS), the risk of gene transfer from corn and soybeans "to sexually compatible plants that results in the generation of progeny that can persist in the environment is negligible" in the U.S. This also is the case with cotton, potatoes, tomatoes and tobacco. Al-though potato and cotton have wild relatives, wild populations exist only for cotton relatives in the U.S.
APHIS also has determined that these crops listed have no weedy relatives in the U.S.
Margaret Mellon, director of the agriculture and biotechnology program for the Union of Concerned Scientists, an organization dedicated to improving the environment, notes that pollen from transgenic crops can only fertilize related plants growing near the crop. "Corn and soybeans do not have wild or weedy relatives in the U.S. and pose no risk of transferring pollen into weeds here. But crops such as canola and squash do have relatives here and pose risks of becoming weeds."
Mellon is coauthor of The Ecological Risks of Engineered Crops, which lists crops with wild and weedy relatives. The book also discusses crops that are more likely to be converted to weeds through genetic engineering.
Mellon adds that although some crops pose no risks in the U.S., they may pose weediness problems elsewhere. "Corn, for example, has an important wild relative in Mexico and Guatemala called teosinte," she says.
Figuring the odds. USDA's APHIS has procedures that it claims will guard against the potential for transgenic crops to become weed risks. Developers of herbicide-resistant crops must fulfill notification requirements to introduce certain genetically engineered organisms in corn, soybeans, cotton, potatoes, tomatoes or tobacco. Developers also must meet requirements in their petitions to receive release from regulation of such plants that do not present a plant pest risk.
Companies intending to commercialize transgenic products conduct risk assessments, which are reviewed by APHIS. James White, senior operations manager, USDA-APHIS, says transgenic field tests are conducted under the guidance of APHIS.
Agriculture and Agri Food Canada has research stations across Canada. This agency has worked with the University of Saskatchewan on the biology of canola, including this crop's outcrossing behavior, says Margaret Gadsby, director, regulatory affairs-biotechnology, AgrEvo. She adds that companies such as AgrEvo will conduct additional research to verify that their transgenic products will behave as expected. Developers are trying to characterize their products appropriately and earn government approval, she says.
Gadsby notes that if a company were to alter a crop's reproductive processes in any way, such as changing duration of fertility or pollen size, an effect on outcrossing might be possible.
Gerry Dill, research director, global product stewardship, Monsanto, says that his company assesses the potential for outcrossing using greenhouse and small plot tests. Researchers observe pollen flow in these test environments if risk information is not already available. They pay particular attention to crops in geographies where outcrossing is known to occur. In Canada, Monsanto is conducting numerous tests on canola plots that are planted for commercial demonstrations.
Reducing the risks. "We're doing a lot to understand the impact of transgenic traits, and this differs by crop," Dill says. He notes that Monsanto weighs the impact of transgenic crops before introducing them and also determines what control measures may be used to mitigate resistance response.
Jeff Stein, director of regulatory and government affairs, Novartis Agribusiness Research, says that the industry is putting the finishing touches on a standard insect resistance management program. He notes that growers will be able to practically (and economically) implement the plan to prevent corn borers from building resistance to Bt. The plan, which should be ready in 2000, includes mitigating measures "in the unlikely event that resistance to Bt were to develop," Stein says.
Developers of transgenic crops are very aware of the potential of resistance buildup in weeds and pests, says Greg Wandrey, corn marketing manager, North America, Pioneer Hi-Bred International. "We know it is important to monitor changes that may occur and to have multipronged approaches to control the pests that growers deal with. For example, we continue to look for and we have found several modes of action that control corn borer. These developments, along with good insect-resistance management, education and implementation of plans, are important factors in decreasing potential risks," Wandrey says.
"Major land grant universities have programs devoted to the study of resistance management," adds Scott McFarland, director of industry relations, National Corn Growers Association. In addition to weed research programs, there are extension programs dedicated to studying the management of corn borers and rootworms, he says. USDA's White adds that USDA has provided grants to universities to make risk assessments.
Universities are well aware of public perception as well as the scientific aspects of resistance, says Ian Heap, WeedSmart, Corvallis, OR. He adds that universities have invested a considerable amount of money in the study of transgenic crops and resistance.
Companies that are developing herbicide- and insect-resistant products share information with the appropriate regulatory agencies during the commercial registration process. Even so, McFarland has some reservations. "I'm concerned that biotechnology companies are rushing some transgenic crop products to the marketplace because Wall Street rewards their stock price every time a new product gets registered and released. The impatient bulls on Wall Street are demanding return on the billions of dollars of investments they've made in big-business biotech over the past decade. The pressure to put new products on the market as soon as possible may cloud some biotech companies' judgment regarding the potential for resistance."
McFarland continues, "Another concern I have is the fact that different companies produce different research results regarding the potential for resistance. Companies always believe their internal research, which may not include all variables that could impact resistance."
White says growers must consider the many variables that can affect plants. Moreover, it is difficult to predict what may happen when a product has been tested on 10,000 acres but may eventually be grown on a million or more acres. White cautions that some growers may be too ready to plant products that have not been fully tested in their area.
Stacked traits. The market will increasingly see crops with stacked traits. Could the potential for resistance be greater with their introduction?
"Current science suggests that it might be less," McFarland says. "Theoretically, stacked strategies employ multiple modes of action, thus increasing control. With this increased control, survival of the targeted pests should be zero."
However, the Union for Concerned Scientists' Mellon says, "It seems reasonable that weeds that are both herbicide tolerant and equipped to fight off pests could be more of a problem than weeds with only one additional trait. But much depends on whether the weeds would be subject to herbicides and/or certain kinds of pests. Plants with stacked traits aren't necessarily going to become 'super weeds,' but might have a greater chance than single-trait transgenics."
Oregon State University's Heap says that a crop with several herbicide-tolerant traits stacked together could have more potential for becoming a weed itself (volunteer). This would be more likely to happen than a transgenic crop's conferring resistance to other plants.
USDA's White says the potential for resistance in a product with stacked traits is still unknown. "That's why we do evaluations on a case-by-case basis," he says. He adds, however, that most plants are resistant to most pathogens. "Susceptibility is the exception."
Ask questions. If you are concerned about the risk of passing on resistance, talk to your seed suppliers. "Farmers should ask if extensive and complete research has been conducted relative to the potential for resistance to develop. They also should inquire as to whether an unbiased third party has evaluated the findings," McFarland advises.
Adds Mellon, "Farmers should ask whether the crops have wild relatives in the region and how far away from the crops the weeds must be to avoid pollen transfer."
Bob Hartzler, extension weed management specialist at Iowa State University, advises growers to consider how the introduction of herbicide-resistant crops will affect their herbicide choices. If they are using Roundup on both corn and soybeans, for example, growers may increase the likelihood of volunteer corn in their soybean fields, Hartzler notes. This may force growers to use herbicides other than Roundup for soybeans. Hartzler points out that there are several other corn herbicide options.
AgrEvo's Gadsby says that companies "are happy to expound" on transgenic products and welcome customer questions about such issues as volunteer crops and crop and/or herbicide rotations. Good questions, she says, would be, Is there anything I should do with this crop that is different from practices used with conventional crops? and What are the warning signs that I have a resistance problem?
Pioneer's Wandrey says that the use of good pest management practices is critical for keeping resistance at bay. These include using different or rotating modes of action, implementing cultural practices and using common sense.
Gadsby agrees. She advises that if a grower notices a patch of weeds that is not responding to herbicide treatment, he should get on the phone right away. A company representative will likely come out and see if there is a potential resistance problem or if the situation is due to something else. Either way, it makes sense to address the situation in a timely manner.
Growers should ask companies about any special management requirements associated with transgenic crops, Gadsby says. She suggests that growers make their product selections based on their management level. If they learn that some new technology requires more management than they are willing to do, they may want to consider another product.
Wandrey states, "It is important for industry, universities, agricultural organizations and growers to work together to understand factors that can potentially lead to resistance and use practices that minimize the probability of resistance."