10
Dec
Herbicide (Dicamba) Drift Adversely Affects Non-Target Pollinators and Plants
(Beyond Pesticides, December 10, 2015) Researchers at Pennsylvania State University (Penn State) and the Pennsylvania Association for Sustainable Agriculture published a study, which found that aerial drift of the herbicide dicamba adversely affects non-target plants and pollinator species. Dicamba is a chlorinated benzoic acid herbicide associated with neurotoxicity and reproductive effects. The study used alfalfa crops to track the flowering and floral visitation by insects, specifically pollinators, after applications of sublethal doses of dicamba. The researchers concluded, “Our results suggest that widespread non-target damage from these herbicides may adversely affect pollinator communities.”
Because dicamba is “frequently responsible for sublethal, off-target damage” to plants and insects, Penn State researchers assessed the most common route of exposure: particle and vapor drift. In its study, Effects of the Herbicide Dicamba on Nontarget Plants and Pollinator Visitation, the research team examined the crop species alfalfa (Medicago sativa), which requires insect pollination to produce seeds, and the native plant species common boneset (Eupatorium perfoliatum), which is highly attractive to a wide range of pollinator species. The researchers applied a range of sublethal doses of dicamba to the plants, then tracked flowering and floral visitation by insect species. They identified the types of insects visiting the flowers and analyzed pollen quality to determine if herbicide exposure altered pollen quality. “We found that both plant species are susceptible to very low rates of dicamba — just 0.1 to 1 percent of the expected field application rate can negatively influence flowering,” said John Tooker, Ph.D., entomologist and extension specialist at Penn State. “This will lead to higher levels of non-target damage to susceptible crop plants and native, wild vegetation”¦For non-crop plant species, this drift-induced damage could significantly decrease the pollinator and natural enemy communities that these plants can support,” he explained.
“Because of the challenge of glyphosate-resistant weeds, new types of transgenic crops that are resistant to synthetic-auxin herbicides including dicamba and 2,4-D will be widely planted in coming growing seasons, raising concerns about damage from these drift-prone herbicides,” said Dr. Tooker. Herbicide currently accounts for 50% of pesticide use in the United States. “The expected high rate of adoption of the new transgenic crops will increase dicamba and 2,4-D use by four to eight times.
Dicamba and 2,4-D are synthetic-auxin herbicides, meaning they mimic plant growth hormones, disrupting natural plant processes. According to David Mortensen, Ph.D., professor of weed and applied plant ecology at Penn State, “Synthetic-auxin herbicides are usually used early in the growing season, but with the new transgenic crop varieties coming on the market, these herbicides will be used later when temperatures are warmer and more plant species are leafed out.” This could also increase the possibility that bees encounter these herbicides or the plants affected by them.
Studies like this one are imperative to position the safeguards needed to protect pollinators and the crops dependent on their pollination. According to a 2012 study, pollination services for all crops requiring direct pollination annually exceed $15 billion, and wild bee communities provide nearly $3.5 billion worth of these pollination services. While neonicotinoids (neonics) have been the focus of the pollinator decline discussion, other pesticides have been found to adversely affect pollinators. A recent study conducted by Germans and Argentinian researchers found that honeybees exposed to low doses of glyphosate have a hard time returning home.
Glyphosate used in herbicide-tolerant crops, has resulted in the creation of GE crops resistant to chemicals like dicamba and 2,4-D. Because of glyphosate overreliance, there are at least 29 weed species worldwide that are resistant to glyphosate. Previously, “Roundup Ready” crops were thought to make herbicide application easier; instead, it inadvertently created a resistance that led to new GE crop systems, like Enlist Duo (glyphosate and 2,4-D). Because weeds have mutated to tolerate almost every form of herbicide weed control system sent their way, farmers are experiencing problems with super weeds and, in turn, invest in chemical-intensive systems that harm human health and the environment.
As the crisis in weed resistance escalates, threatening crop productivity and profitability, advocates point to organic agriculture as a solution that protects public health, the environment, pollinators, and farmers’ livelihood. Ecological pest management strategies, organic practices, and solutions that are not chemical-intensive are the most appropriate and long-term solution to managing unwanted plants, or weeds. Additionally, organic agriculture is an ecologically-based management system that prioritizes cultural, biological, mechanical production practices, and natural inputs. By strengthening on-farm resources, such as soil fertility, pasture and biodiversity, organic farmers can minimize and even avoid the production challenges that most genetically engineered organisms have been falsely-marketed as solving. To learn more about organic agriculture, see Beyond Pesticides Organic Program Page.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Pennsylvania State University
