Pesticides can contribute to the major problems with certain weeds

A study led by researchers in Pennsylvania found that pesticides may help growers who want to protect their crops from harmful insects, but they may also contribute to more weeds.

This study was published in the PEERJ Journal – compared to using an integrated pest management (IPM) approach using insecticides at planting, it only requires insecticides when known insect problems are present.

The team also investigated the impact of using cover crops, which are crops used to cover and protect soil after harvesting cash crops, when combined with these treatment plans.

By the third year, researchers found that some areas that had been treated with insecticides and had no cover crops ended up with a slightly more weed, especially malesteil. However, planting cover crops prevented this problem even in pesticide-treated fields.

John Texer, the paper author and professor of entomology at the University of Agriculture Sciences, said that he and other researchers are not sure what caused these findings, but the most likely explanation is that preventive insecticides usually eat weeds and weed seeds, limiting the activity of insects that make us eat more quantities.

He added that while the findings could help growers develop management plans for their field, it makes sense to use herbicides, insect pests are less common as weeds are a very widespread problem.

“Always using pesticides in planting doesn’t seem to be the best approach in Pennsylvania given that early seasonal insect pests tend to be a relatively rare issue,” Take said. “When taking the IPM approach, we advocate for the use of the right products at the right time to control the right pests, and it also helps to reduce these negative consequences of using too many of these treatments.”

Elizabeth Lowen, lead author and assistant professor at the University of California Riverside, said the findings are particularly relevant because weeds are increasing tolerance due to glyphosate, a commonly used herbicide.

“Many of the seeds used by growers have been developed to prevent herbicides from being killed,” she explained. “This allows growers to control weeds using glyphosate, but this leads to the evolution of herbicide-resistant weeds, making it much more difficult to control weeds without killing crops.

Insects such as beetles, ants, and cricket eat weed seeds. However, pesticides can affect these beneficial insects in addition to pests, which can interfere with their ability to eat these seeds and control weed populations.

In this study, the researchers used plots to grow corn and soybeans at the Russell E. Larson Agricultural Research Center, Pennsylvania. They assigned one of three treatment plans for each plot. This is an IPM treatment plan that uses a preventive insecticide during planting and uses insecticide only if the pest has reached a certain threshold, or if there is no insecticide at all. The team also tested each treatment with or without cover crops.

The researchers then looked at the plot over three years, noting several factors along the way, including covering biomass, predator insect communities, weed seed predation, weed populations, and crop productivity.

Teaker said the study provides evidence that the IPM approach is valuable to growers, especially those with large area systems.

“Popular and soybean fields are often so large that growers tend to do all their management in advance, so there’s no need to go back and walk through the fields,” he said. “However, our evidence suggests that identifying the problems to walk through these fields can provide a clear advantage in that it does not require specific pesticides.

Kirsten Ann Pearsons, IPM coordinator at T&L Nursery, received his PhD in Entomology from Pennsylvania. Richard Smith, University of New Hampshire. Kyle Wicking of Cornell University also co-authored the study.