Practices can prevent or delay the rise of resistant weeds, pests

By MATEUSZ PERKOWSKI

Capital Press

Transgenic crops have helped reduce erosion and the use of toxic pesticides, but injudicious use of biotechnology could cause these environmental benefits to fade, according to a genetic engineering expert.

As novel crop traits are developed to aid in producing pharmaceutical and industrial materials, the agriculture industry will need be particularly careful to mitigate against unintended consequences, said Yves Carriére, an entomology professor at the University of Arizona.

"The risk is there. The escape of transgenes can occur," he said. "You don't want insulin in your tacos."

Carriére, who has studied the environmental impacts of biotech crops for the National Academy of Sciences, recently lectured on the subject during a visit to Oregon State University.

Genetic engineering is most prevalent in soybeans, corn and cotton, with biotech traits focused on herbicide and insect resistance, he said.

The popularity of glyphosate-tolerant crops has caused that chemical to greatly offset the usage of other herbicides that are more toxic to mammals, birds and fish, Carriére said.

Using glyphosate to kill weeds has also encouraged farmers to adopt conservation tillage practices that decrease soil disturbance, he said. "They can reduce erosion, increase water infiltration in fields and reduce runoff of sediments."

However, the continued reliance on glyphosate is rendering the herbicide less efficient by promoting weeds that are resistant to the chemical and allowing them to proliferate, Carriére said.

Over time, the rise of glyphosate-resistant weeds will likely prompt farmers to return to conventional tillage and other herbicides unless they are proactive in diversifying their weed strategies, he said.

Biotech companies have asked the USDA to deregulate several crops that can tolerate other herbicides, such as 2,4-D and glufosinate, to fight glyphosate-resistant weeds.

Carriére said he'd prefer farmers not to use a tank mix of glyphosate and other herbicides, as this would eventually lead to weeds resistant to several chemicals.

Rather, farmers should rotate through the chemicals, using a different one each year to prolong their effectiveness, he said. "Then we're in business."

Crops that incorporate genes from the soil bacteria Bacillus thuringiensis, or Bt, to ward off insect pests face the same challenge, though the consequences so far have been small, Carriére said.

Planting "refuges" of non-Bt crops can slow resistance in insects, as pests from these fields will mate with resistant ones, he said. Since the resistance gene is recessive, this strategy will reduce the heritability of this trait.

Biotech traits that make crops more competitive, such as drought or salt tolerance, also pose a risk because they can confer those advantages to weeds, Carriére said.

With corn and soybeans, this risk is negated by the fact these crops are grown in areas without sexually compatible weeds, he said. For crops like canola, though, the risk of gene flow is significant.

One possible solution may be to develop biotech crops in which the novel traits don't work until they're activated with a spray, preventing weeds from benefiting from those properties, Carriére said.

The Center for Food Safety, a group that opposes many biotech crops, disagrees with the notion that genetic engineering has helped the environment with increased conservation tillage.

Such conservation efforts predate the widespread cultivation of biotech crops, and were driven primarily by federal subsidy incentives in the mid-1980s, said Bill Freese, the group's science policy analyst.

Farmers who have already decided to use conservation tillage may then plant herbicide-resistant crops, but they're unlikely to adopt such practices because of biotech crops, he said.

The prevalence of biotech genes is also making it harder for farmers to plant refuges of non-Bt crops, increasing the risk of insects becoming tolerant to Bt, Freese said. "It's getting really hard to find conventional corn."