Increasing Herbicide Use
Roundup resistance has led to greater use of herbicides, with troubling implications for biodiversity, sustainability, and human health
Monsanto’s Roundup Ready system, which involves applying glyphosate (Roundup) herbicide to crops genetically engineered to tolerate it, was supposed to decrease overall herbicide use—and for a while, it did just that. However, this has changed drastically in recent years.
A Butterfly Effect?
It is not only older, more volatile herbicides that can cause sustainability problems—widespread use of glyphosate can do damage in its own right.
For example, Roundup's effectiveness (when resistant or tolerant weeds are not present) has an unfortunate consequence: glyphosate kills milkweeds in and near corn and soybean fields that were able to survive other herbicides.
These milkweeds were probably not present in high enough quantities to cause substantial crop yield loss, so there is no significant benefit to killing them—but they are the required food of monarch butterfly larvae, and therefore a critical part of the annual monarch migration through the U.S. Midwest.
Several recent studies show a decline in milkweed in the Midwest, traceable to increased glyphosate use—and corresponding to recent lower monarch numbers. Although more research is needed, this loss of food supply may be one of the factors putting pressure on monarch butterfly survival.
As we've already seen, the number and extent of resistant weeds have increased dramatically over the past decade. At the same time, some Roundup-susceptible weeds have been replaced by weeds inherently less easy to control with glyphosate. The result has been an increase in overall herbicide use—recently estimated at about 383 million pounds higher than would have been the case without Roundup Ready crops.
Meet the New Herbicide,
Same as the Old Herbicide
Monsanto’s proposed solution is to develop and seek regulatory approval for new engineered herbicide-tolerant crops to augment Roundup Ready crops. Predominant among these new engineered crops are those with resistance to two of the oldest herbicides, 2,4-D and dicamba.
These herbicides may be more harmful in some respects than glyphosate. Both become volatile after application, which means they can spread to nearby wild vegetation—important for biodiversity and natural pest control—and to other susceptible crops.
There is also evidence that 2,4-D may increase the risk of some types of cancer.
More Herbicide = Less Biodiversity = More Insecticide
Because of the volatilization problem, increased use of the old herbicides may also harm neighboring crops that are not resistant to them—including locally grown fruits and vegetables.
A recent article estimates that risk to plants surrounding sprayed fields is from 75 to 400 times greater for the older herbicides than for glyphosate. The industry is working on formulations of these herbicides that may be less volatile, but that is unlikely to eliminate the problem—especially because the use of these herbicides is projected to increase tenfold.
Damage to plant biodiversity near crop fields may also reduce the abundance and diversity of beneficial organisms that thrive in those habitats (but not in monoculture crop fields). Recent research has shown that when agricultural landscapes are simplified by the reduction of plant and beneficial organism diversity, much more chemical insecticide is needed to control pest insects.
So if the volatilization problems are not eliminated, this “solution” to glyphosate resistant weeds may make matters worse, and may also lead to increased insecticide use—and possibly greater risk to people, especially farmers and farm workers.