What Would Happen if We Stopped Controlling Weeds? July 19, 2018
If you are a farmer, the idea of purposively not controlling weeds might seem like a silly proposition, but the question has been asked before. A few years ago, a county in a neighboring state was debating banning the use of genetically engineered crops on county-owned land. Several farmers leasing county-owned land risked being prohibited from using glyphosate for weed control in their sugarbeet crop. During the public discussion, a concerned citizen asked if any of the farmers had tried not controlling their weeds. Maybe, this person advanced, maybe weeds would just go away on their own if we just stopped trying to control them. While I do not believe there has been a study on whether weeds will decide to just go away, we do have a fairly good idea of what happens when a weed control strategy is “do nothing.”
Weed scientists generally want a weed control program to provide 95% control of weeds for it to be considered a good program. To determine the level of weed control a program provides, each weed control trial needs to include a “non-treated check” treatment. In the “non-treated check” plots, the crop is planted and no weed control measures are taken. You may have seen those plots before. They stick out in a field as wild, messy, 6-feet-tall weed jungles in perfect rectangles of 10-by-30 feet. We include this treatment to have a good idea of how many weeds are present in the study and what the value of the other weed control treatments are in controlling weeds and preserving yield. Essentially, the non-treated check serves as a baseline to evaluate weed control programs. So what happens when we do nothing to control weeds?
A recent paper titled Potential Yield Loss in Dry Bean Due to Weeds in the United States and Canada and published in the journal, Weed Technology, summarizes weed control data from the past ten years (2007-2016) from weed scientists in Nebraska, Idaho, Montana, Michigan, North Dakota, South Dakota, Wyoming, Manitoba, and Ontario. Every study conducted in the US and Canada that included both a non-treated check and a treatment providing at least 95% weed control was included.
With the data from that paper we can imagine what would happen if we waited for the weeds to leave on their own. If we stopped controlling weeds in dry bean, the average yield loss for all of North America would be 71%, or a loss of 28 million CWT. Financially, this would translate to a $720 million loss (per year) for the US and Canada. Yield loss would not be equally distributed across North America, however. Some regions would be more impacted than others. Michigan reported an average potential yield loss of “only” 31% over the past 10 years, while North Dakota averaged a staggering 93% yield loss. Nebraska was in the midrange of this disastrous scenario, with an average potential yield loss of 58%. The potential monetary loss for Nebraska from not controlling weeds is estimated at $55 million (per year).
While the results of this paper are not surprising, it is good to have science-based data on the value of weed control. Let’s use it to support the efforts of farmers, researchers, and other ag professionals as they battle weeds and a sometimes-misguided public opinion.