A recent study found that while insecticides can protect crops from pests, they might also increase certain weed populations. The research suggests that integrated pest management and cover crops could help mitigate this problem.
Insecticides used to safeguard crops from pests may inadvertently lead to increased weed growth, according to new research. The study, published in the journal PeerJ, compared preventive insecticide use at planting with an integrated pest management (IPM) approach, which only uses insecticides when a significant insect threat is present.
The researchers also evaluated the impact of cover crops — plants grown to protect and enrich the soil after harvesting the main crop — on the effectiveness of these pest control methods.
The study found that by the third year, fields treated with insecticides and lacking cover crops experienced a slight increase in weed population, particularly marestail. Conversely, fields with cover crops did not exhibit the same weed issues, even when treated with insecticides.
John Tooker, professor of entomology at Penn State’s College of Agricultural Sciences and a co-author of the study, suggested that the preventive insecticides might hinder insects that naturally control weed seeds, thus allowing weeds to proliferate. He emphasized the importance of this finding for agricultural management.
“Always using an insecticide at planting does not seem to be the best approach in Pennsylvania considering that early-season insect pests tend to be a relatively uncommon problem,” Tooker said in a news release. “When taking an IPM approach, we advocate for using the right products at the right time to control the right pests, and that will also then help reduce these negative consequences of using these treatments too much.”
Lead author Elizabeth Rowen, an assistant professor at the University of California, Riverside, highlighted the relevance of these findings amid increasing resistance to glyphosate, a widely used herbicide.
“Many of the seeds growers use were developed to not be killed by herbicides,” she said in the news release. “This allows growers to use glyphosate to control weeds; however, this also results in the evolution of herbicide-resistant weeds, which makes it much harder to control weeds without killing the crops. So, having multiple strategies to help manage weeds is really important.”
The study examined how prevention-focused and IPM treatment approaches impact predator insect communities, weed seed predation, weed populations and crop productivity.
Using plots of corn and soybeans at Penn State’s Russell E. Larson Agricultural Research Center, the researchers assigned them one of three treatment plans: preventive insecticide use at planting, an IPM approach, or no insecticides. Each treatment was also tested with and without cover crops.
The team found that utilizing an IPM approach could benefit growers, particularly those managing large acreage systems.
“Oftentimes corn and soybean fields are so big that growers are inclined to do all of the management up front so they don’t have to go back and walk the fields,” Tooker added. “But our evidence suggests that walking these fields to identify problems as they happen can provide clear benefits in terms of not needing certain pesticides, namely many of the fungicides and insecticides.”
Co-authors of this study include Kirsten Ann Pearsons, a former doctoral student from Penn State and now an IPM coordinator at T&L Nursery, Richard Smith from the University of New Hampshire and Kyle Wickings from Cornell University.