By Mary Lou Peter
Imagine that weeds were left to grow uncontrolled in corn and soybean fields across North America. That scenario would cut U.S. and Canadian yields by about 50 percent, resulting in $43 billion in annual economic losses to those two crops alone, according to a new study.
The research, conducted by the Weed Science Society of America and led by K-State weed scientist Anita Dille, spanned seven years from 2007 to 2013. Details about the study are available at Crop Loss.
“We were interested in trying to understand just how much impact weeds still have on our crops. Despite the great improvements we have in crop genetics and fertility, we’re still having to manage weeds,” Dille said, noting that weeds compete with crops for everything from sunlight to moisture to nutrients in the soil.
Dille explains the findings in a short Youtube video from Dan Donnert, K-State Research and Extension videographer, at: https://youtu.be/F4R_AP4LKGU
Figure 1. Weeds are still a significant pest to manage, and we need to maintain all the different weed control practices that we have, says Anita Dille, K-State weed scientist.
“What we saw in corn is that we’d lose over half of our yield if we didn’t manage those weeds – a 52 percent yield loss,” Dille said. “And in soybeans, almost the same – 49.5 percent total yield loss on average.
According to the Weed Science Society of America study, Kansas alone would potentially have lost 52.6 percent of soybeans at an average financial cost of $666,435 per year over the seven years of the study (2007-2013) if weeds had been left to grow unchecked.
The study indicated a potential yield loss of 46.3 percent of dryland corn per year at a value of just over $500,000 without any sort of weed management.
“We wanted to document that weeds were still a significant pest to manage, that we need to maintain all the different weed control practices that we have. There’s a lot of pressure on the industry to say, ‘hey, stop doing this or that.’ We wanted to highlight that these weeds are still so important and that we need to come up with every option that we can to manage them.”
A recent dramatic reduction in research funding for weed management in crops is a trend she and other scientists find disturbing.
Weed scientists conduct a number of weed control studies each year, Dille said, so the WSSA team asked them to provide the yield data from corn and soybean trials, specifically the untreated plot yield, and yield from plots with their best weed control methods. The team looked at the yields from both and took the difference to calculate how much yield loss happened.
“So, the idea,” she said, “was they did everything right to produce their best crop – their best seed, they fertilized it, they irrigated it – whatever they needed to do, but they just didn’t control the weeds in the untreated plots, so we could see what kind of yield loss impact that would have.”
Figure 4. Plots with uncontrolled weeds and plots with good weed control. Source, K-State Research and Extension video: https://youtu.be/F4R_AP4LKGU
In comprising the WSSA report, the scientists used data from these trials, plus the U.S. Department of Agriculture’s National Agricultural Statistics Service and Statistics Canada on how many acres were harvested of those crops and the value of the crops over the years studied to determine the total potential impact of weeds on the crops.
Dille likes to break weed management into four categories: