Carbondale, IL. - When it comes to using a popular herbicide method, it's more about the where than the what, according to a recent study led by researchers from Southern Illinois University Carbondale.
The study showed that cropping methods using the popular herbicide glyphosate in conjunction with genetically engineered plants has less effect on the diversity of the weed population than their geographic location.
A leading plant science group and journal is honoring four present and former researchers at SIU for their article on the study, which looked at the effects of certain herbicides on plant diversity.
The Weed Science Society of America, which publishes the scientific journal Weed Science, named "Seedbank and Field Emergence of Weeds in Glyphosate-Resistant Cropping Systems in the United States" as its Outstanding Paper of 2015.
Lead author of the article was Lauren Schwartz, a doctoral alumna in plant biology who at the time was a doctoral student at SIU. Additional SIU authors included David Gibson, professor of plant biology; along with Karla Gage and Joseph Matthews, assistant professor and assistant scientist, respectively, of plant, soil and agricultural systems, along with colleagues from other universities. Bryan Young, formerly of the College of Agricultural Sciences at SIU, was the lead investigator on the study on which the article is based.
Schwartz accepted the award on behalf of the researchers during the annual meeting of the society earlier this month in Puerto Rico.
Gibson said the study was one of a one of a series of papers to emerge from the so-called "Benchmark Study," a large, multi-investigator study on the effects of glyphosate-resistant cropping systems on various aspects of agricultural production. Glyphosate is one of the most commonly used herbicides in the world and certain crops contain a genetic trait that makes a crop resistant to its herbicidal effects, allowing farmers to use it to kill weeds without harming the crops.
Plant and agricultural scientists and others are concerned about weeds evolving to develop resistance to glyphosate, as well. The study attempted to answer some of that concern by looking at what factors had different effects on the weed population at various sites.
The overall objective of the Benchmark Study was to determine how the use of these glyphosate-resistant crops may influence any change in weed populations found in commercial production fields operated by individual farmers, Gibson said. The study on which the article was based looked at this issue in 156 different fields across six Midwestern states
"In this particular study we were trying to find out how the seed bank – the underground reserve of viable weed seeds – might be affected by the glyphosate cropping systems used across a large part of the Midwest," Gibson said.
Researchers took soil samples from the fields and then grew the seeds they contained in a greenhouse, identifying the weeds that emerged. They then compared the results with data on the weeds that were growing in the fields, the soil texture, irrigation, herbicide application and other factors. They also examined the type of glyphosate cropping system being used, such as a whether it contained a single, continuous glyphosate-resistant crop, a rotation of two such crops, and such a crop rotated with a non- glyphosate-resistant crop.
The team was able to identity 139 different species of weeds from 150 sample field sites. They found a large geographic variability, with 79 species unique to a single state. Some of the most troublesome agricultural weeds stored seeds in the soil, including common water hemp and redroot pigweed, Gibson said.
The research yielded some interesting findings, in that the team found the composition of the weed seed bank was most closely related to the location where the sample was collected and that area's climate, as well as the weeds recorded growing in the field. Those factors were more strongly related to the seed bank composition than the glyphosate cropping system in use at each site.
"In other words, the effects of weed management practices are likely to operate on a small, perhaps individual farm scale rather than be generalizable across the whole Midwestern U.S.," Gibson said. "The evolution of herbicide-resistant weeds is a particular concern, and our findings suggest that increasing crop diversity, rather than moving away from the glyphosate-resistant trait in crops, may not alter the composition of weeds in crop fields, and may have the best impact on deterring evolution of (these) weeds."
Gibson said the research provides another window into the practice of sustainable farming methods and that its large scale may account for the honor from the Weed Science Society of America.
"Although I don't know the exact reason why the journal selected our paper for this honor, I can only assume that they recognized this research was conducted on the largest scale to date for addressing weed population dynamics in agricultural sites," he said. "I believe it represents a thorough and well-researched study of an important and timely topic. Certainly, there is a lot of interest in scientific circles, among growers, industry, and the general public on the effects of herbicides on the environment. We hope that it contributes to the debate on sustainable farming practices."