Grower acceptance of genetically engineered (GE) corn, soybean and cotton has certainly been dramatic since the introduction of this technology 13 years ago. Many growers have used these herbicide and insect traits to boost yields while reducing production costs with more environmentally friendly farming practices.
A July report from the U.S. Department of Agriculture’s Economic Research Service indicates that the percentage of soybean acres planted with herbicide-tolerant traits increased from 54% in 2000 to 91% in 2009.
During the same period, corn acres planted with one or more GE traits increased from 25% to 85%. In 2009, 17% of the acreage was planted with insect-resistant Bt hybrids, 22% with herbicide-tolerant hybrids and 46% with stacked hybrids that include both herbicide- and insect-resistant traits.
While the acreage of herbicide-tolerant crops continues to grow, weed scientists continue to voice concerns about the growing impact on resistant weeds and the reluctance on the part of growers to use alternative herbicides. While growers are sold on this weed-control chemistry, overuse may force the industry to develop new approaches to weed control.
To overcome a growing concern about weed species becoming immune to glyphosate, weed specialists in a half-dozen states recently released a study on glyphosate resistance management strategies. Some 1,200 growers in these states were asked how they used glyphosate and when they applied the herbicide.
The major use of glyphosate was as a burndown application with cotton and soybeans. Between 54% and 63% of growers made one or two post-emergence glyphosate applications in continuous corn or a corn-soybean rotation. Up to 62% of Roundup Ready soybeans received a double application of glyphosate, while less than 42% of Roundup Ready corn received a second dose.
Only 16% of the growers used a non-glyphosate herbicide in Roundup Ready beans while 40% of Roundup Ready cotton acres received up to three glyphosate applications.
Two-thirds of the growers felt weed pressures in some fields declined with glyphosate use. However, nearly half of the growers felt weed pressures remained the same in some fields.
A few growers even indicated that weed pressures increased with the use of glyphosate, which means they may already have weed resistance.
The study also found that glyphosate was the major reason why the number of no-till growers in recent years jumped from 25% to 41% in these states. Some 92% of farmers who no-tilled prior to using glyphosate have stayed with the practice. Among farmers previously using conventional tillage, 25% shifted to no-till and 31% shifted to other reduced-tillage systems after adopting glyphosate.
While educators and the chemical industry have talked about weed-resistance concerns, another study indicated that only 30% to 40% of farmers were aware of glyphosate-resistant weeds in their area. Less than 30% believed glyphosate resistance was a serious agronomic issue.
While 19% of growers reported some weed resistance, only two-thirds had done anything about it.
In another new study, weed scientists have created 25-acre test plots on 150 farms across the Midwest. Each grower is following his current herbicide program on half of the plot while researchers manage the other half of the plot with a program that is designed to reduce the potential for glyphosate resistance with possible use of several alternative herbicides.
The results will provide valuable data on properly developing effective weed-resistance strategies.
In summary, it’s time to make more careful use of these genetically engineered traits or face the fact that insect and weed resistance will continue to grow.
Avoiding overuse is a serious concern that only you can solve.