10
Apr
Scientists Determine the Only Solution to Herbicide Resistant Weeds Is to Reduce Herbicide Use
(Beyond Pesticides, April 10, 2018) Current strategies aimed at managing herbicide resistant weeds in agriculture are not effective and may exacerbate weed problems, according to research published earlier this year by scientists at University of Sheffield in the United Kingdom (UK). While the conventional wisdom in farming, promoted strongly by the chemical industry, is that resistance can be adequately managed by rotating the herbicides used, researchers did not find evidence to support this strategy. In an ode to Occam’s razor, a philosophical theory that hypotheses with the fewest assumptions may be the correct one, researchers found the best method to reduce weed resistance to herbicides was to reduce the overall use of herbicides.
Sheffield scientists focused their research on the occurrence of a common weed in the UK called black-grass. This weed was found to occur on 88% of the farmland tested in the study, and has recently been spreading into new areas it had never before colonized. Rob Freckleton, PhD, a population biologist and co-author of the study indicated to Science Daily, “The driver for this spread is evolved herbicide resistance: we found that weeds in fields with higher densities are more resistant to herbicides.”
Thus, the more abundant black-grass was found to be, the more researchers found resistant versions of the plant. The study investigated a range of factors that may be related to herbicide resistance, including management techniques that switch up herbicides used, or plant different crops. However, resistance was linked solely with how often and how much herbicide was used on a particular farm. Dr. Freckleton explains to Science Daily, “The results were simple: farms that used a greater volume of herbicide had more resistance. Beyond this we found little evidence for a role of any other management techniques: neither the diversity of chemicals used — for example whether farmers used a variety of herbicides or just one — or diversity of cropping mattered, despite both being advocated as methods to reduce the evolution of resistance.”
Scientists are confident in this determination because, over the course of the study, weed abundance did not change, despite farmers changing cultural practices. “Once resistance has evolved it does not seem to go away,” Dr. Freckleton said. “Two years later, fields with high densities still had high densities, despite farmers employing a suite of different management techniques.” As far as switching to another herbicide, researchers found that, once black-grass evolved resistance to one herbicide, it became much more likely to develop resistance to other herbicides.
The data implies that these ineffective measures may in fact be hurting farmer’s wallets. “We estimate that the economic costs of this are very high: the costs of weed management have doubled as a consequence of evolved resistance,” Dr. Freckleton notes.
Although weeds on farms using genetic engineering (GE) were not investigated as a result of a UK ban on growing such crops, the study is instructive for herbicide use on these farms in the U.S. Study after study has found that GE crops lead to increased use of toxic herbicides in attempts to control resistant weeds. And now, data finds the industry’s “solution” – namely, adding new, different herbicides to the mix, such as 2,4-D and dicamba, is not only an ineffective method that further endangers public health and neighboring cropland, it is likely going to cost farmers even more as it does nothing to address the fundamental issue causing resistance.
The good news is that the answer to this problem is as simple as understanding it: to limit herbicide resistance, reduce herbicide use. As Dr. Freckleton explains, “This is evolved resistance: when we manage natural systems in a selective manner, evolution is inevitable.” To manage resistance for the long term, organic agriculture has shown a viable path forward. Organic production reserves even the use of least-toxic herbicides to only when they are truly necessary, as a focus is placed on working with, rather than controlling natural systems.
For more information on herbicide resistance, see Beyond Pesticides’ Genetic Engineering program page.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
