Penn State study reveals pea cover crops may boost indirect pest control by attracting beneficial predators while reshaping plant defence chemistry.
The choice of cover crop may do more than improve soil health and nutrient cycling. New research from Penn State’s College of Agricultural Sciences suggests it can also influence how crops defend themselves against insect pests, creating opportunities for farmers to enhance biological pest control through management decisions already common on many operations.
Published in the journal Basic and Applied Ecology, the study examined how different cover crops affect the defensive chemistry of corn plants and the behaviour of insects that interact with them. The findings indicate that cover crop selection can alter both direct and indirect plant defence mechanisms, potentially influencing pest populations and the predators that feed on them.
Researchers focused on three cover crop species commonly used in agricultural systems: pea, radish and triticale - a wheat-rye hybrid. Corn was subsequently grown in soils previously occupied by each cover crop and compared with corn grown in fallow soil.
The results showed notable differences in how the corn plants responded.
Corn grown in soil previously planted with peas released higher levels of indole, a naturally occurring volatile compound that helps plants communicate with neighbours and prepare for insect attacks. Scientists found these plants emitted nearly twice as much indole as corn grown in fallow soil.
According to the research team, indole serves as an early warning signal in plant communities. When released, it can trigger nearby plants to strengthen their own defences by producing stress hormones and protective compounds before significant damage occurs.
At the same time, however, the researchers observed a trade-off. Corn grown after cover crops generally produced lower levels of benzoxazinoids, naturally occurring defensive chemicals that can act as pesticides, fungicides and feeding deterrents.
Jared Ali, associate professor of entomology at Penn State and director of the Center for Chemical Ecology, said the findings provide growers with a better understanding of how cover crop choices can influence crop resilience.
The study offers evidence that cover crops do not simply affect soil conditions. They can also shape the ways plants respond to insect threats, potentially changing the balance between a crop’s direct defences and its ability to recruit help from beneficial insects.
One of the most intriguing findings involved lady beetles, widely recognized as beneficial insects in agricultural systems. When researchers offered lady beetles a choice between fall armyworm larvae feeding on corn grown in different soils, the predators showed a clear preference for larvae found on corn grown in pea-conditioned soil.
Researchers believe the cover crop may have altered the quality of the corn plants and, in turn, affected the quality of the pests feeding on them. That change may have made the caterpillars more attractive to predators.
The discovery highlights the complex relationships between soil conditions, plant health, pest insects and beneficial predators. Rather than acting independently, these factors appear connected through a series of biological interactions that begin below ground and extend throughout the field ecosystem.
Ali noted that scientists have long known cover crops provide benefits such as erosion control, nutrient retention and improved soil health. What has been less understood is how different cover crop species influence future crops growing in the same soil.
The research is part of a broader effort to understand how crop domestication has altered plants’ natural abilities to defend themselves. Over generations of selecting crops for higher yields, improved flavour and other desirable traits, some defensive characteristics may have been reduced.
Researchers are now exploring ways to better utilize the protective traits that remain within modern crop varieties.
For farmers, the findings could eventually contribute to more integrated pest management strategies that combine cover cropping with biological control. By selecting cover crops that encourage beneficial insect activity or influence defensive plant chemistry, growers may gain additional tools for reducing pest pressure while supporting sustainable production.
The research team emphasized that more work is needed before firm management recommendations can be developed. Future studies will investigate the role of soil microorganisms, nutrient dynamics and interactions among multiple species in shaping these outcomes.
Researchers also plan to assess how changes in plant defence chemistry affect important agronomic traits such as crop development and yield. Understanding those trade-offs will be essential to determining whether enhanced pest resistance can be achieved without compromising productivity.
As growers continue to adopt cover crops usage across North America, the study suggests the species selected could have impacts reaching far beyond soil conservation, potentially influencing the entire network of interactions that helps crops defend themselves against insect pests.