Cover crops are more effective than insecticides for pest control, a study shows

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University Park, PA — Promoting vegetation at the beginning of the season, mainly through the use of cover crops, may be more effective in reducing pest density and crop damage than insecticide applications, according to a team from the University of Pennsylvania.

In a newly published study, researchers say the best pest control results can come when farmers promote biological control – in the form of natural enemies of pests – by planting cover crops and avoiding broad-spectrum insecticides as much as possible.

The use of cover crops and other conservation farming practices can help reduce erosion and nutrient loss, improve soil health and improve pest management, said study co-author John Tucker, a professor of entomology at the College of Agricultural Sciences. Penn State. Although acceptance of such methods has increased, he said, pesticide use continues to grow in the United States and around the world, potentially killing non-target, beneficial species and reversing the benefits of pest management from the use of conservation farming tactics.

„The vegetation cover that cover crops create can provide habitat for populations of natural enemies of pests,“ Tucker said. „Winter cover crops, for example, can house predator populations outside the growing season of the main crop. Once the cover crop is terminated to allow the main crop to grow, the remnants of the cover crop remain on the soil during the growing season and improve the habitat for predators.

„Studies have shown that cover crops reduce the insect pest epidemic by increasing the abundance of predators, but to preserve these benefits, it is crucial to protect these predatory species,“ he said.

The aim of this study was to examine how conservation farming practices – cover crops, uncultivated planting and crop rotations – interact with two pest management strategies that use insecticides. These strategies are pest management, in which growers plant seeds treated with a systemic insecticide to control pests in the early season; and integrated pest management, which includes pest research and the use of insecticides only when the number of pests exceeds economic thresholds and only when non-chemical tactics are ineffective.

Predatory beetles peek out of their hole at an experimental plot at the Russell E. Larson Center for Agricultural Research at Penn State. These beetles are responsible for much of the predation observed during the study, but they are mostly nocturnal, the researchers note. Credit: Elizabeth Rowan. All rights reserved.

„We hypothesized that increased vegetative cover at the beginning of the season, provided by winter or spring cover crops, would benefit predator populations and increase their biological control potential,“ said lead author Elizabeth Rowan, a former PhD student. Tucker’s laboratory, which is now an assistant professor of entomology at the University of West Virginia.

„In contrast, we expected that preventive seed coatings, despite reducing the number of early seasonal insects, would also reduce the abundance of predators and release non-insect pests such as snails from biological control,“ she said. „Furthermore, we thought that Integrated Pest Management (IWM) would be as effective as preventive seed coatings for pest management, but with less disruption to the predator community and biological control.“

Researchers set out to study these scenarios by setting up two unprocessed experimental fields at the Russell E. Larson Center for Agricultural Research at Penn State to test the effects of pest management and planting fine-grained cover crops for three years in soybeans. corn-soybeans and rotations corn-soybeans-corn. This experiment was part of a larger project examining the interaction of pest management and cover crops on soil quality, weeds, insecticide movement and pest pressure.

The team divided each field into sections, with six treatments repeated six times in each field over three years. While crop species change annually with rotation, each plot receives the same treatment each year. The researchers looked at three pest management strategies with and without cover crops: preventive seed coatings, IWM and non-pest management.

For the IWM strategy, the researchers studied the IWM insect pest areas and compared the pest populations with economic thresholds to determine if insecticide applications were needed. They used an insecticide – a single application in the furrow of granular pyrethroid – only in the second year of the study.

Researchers who recently reported in the journal Ecological Applications found that the use of each insecticide provided a little reduction in soybean damage, but no yield benefit. The results show that in maize the vegetative cover at the beginning of the season is key to reducing the density of pests and damage.

Cover crops were planted on a farm near Spring Mills, Pennsylvania, in March 2020. Researchers say their new study shows that roof crops may be more effective in pest management than insecticides. Credit: Michael Hautz, College of Agricultural Sciences. All rights reserved.

An unexpected result, the team said, is that the IWM strategy, which requires only one application of insecticides, is more destructive to the predator community than preventive pest management, possibly because the pyrethroid administered is more toxic to a wider range of arthropods than neonicotinoid seed coatings.

„With a single use of an insecticide in IUD treatment, non-target effects persist for more than a year after application, without reducing plant damage or white larvae density, the target pest,“ Rowan said. „This pyrethroid also indirectly reduces soybean yields on IWL plots more than a year later, perhaps due to fewer plant protection predators.

The researchers concluded that planting cover crops and promoting natural enemy populations protect corn and soybeans from damage and that promoting early season coverage is more effective at reducing pest and damage densities than any strategy based on intervention.

„But because cover crops can also leave major crops vulnerable to some sporadic pests, growers need to be careful about choosing the best cover crops for each situation and research regularly for pests in the early season,“ Rowan said. „In addition, maximizing the benefits of cover crops for biological control requires sparing use of insecticides, as preventive use of selective insecticides and reactive use of broad-spectrum insecticides can reduce predator activity without guaranteeing pest control or higher yields. . ”

Other researchers who have contributed to the study include Kirsten Piercens, a former doctoral student in entomology, Penn State; Richard Smith, Associate Professor, Department of Natural Resources and Environment, University of New Hampshire; and Kyle Vickings, Associate Professor, Department of Entomology, Cornell University.

 

The National Food and Agriculture Institute of the United States Department of Agriculture supported this report.