This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Different cover crops may affect how plants defend themselves against pests—including by attracting more insects that eat harmful caterpillars—according to a new study led by researchers at Penn State's College of Agricultural Sciences. The research, published in the journal Basic and Applied Ecology, analyzed the effects and resulting trade-offs of different cover crops, which are plants grown between growing seasons to help protect and enrich the soil.
For example, the team found that plants grown in soil previously used by pea cover crops emitted more of the chemical indole, which primes neighboring plants to defend themselves against insects by enhancing the production of stress hormones and defensive chemicals. However, these plants also had lower levels of benzoxazinoid—a natural toxin present in some plants that can act as a pesticide, antifungal and feeding deterrent. The researchers also found that predator insects preferred to eat caterpillars from corn grown in soil previously occupied by pea cover crops.
Jared Ali, associate professor of entomology, director of the Center for Chemical Ecology and corresponding author on the paper, said the findings offer practical solutions for growers using techniques they're already familiar with. "This allows me to go into the field and tell growers that the cover crops they select changes its potential resistance to pathogens and insects, and that each insect species may respond differently to each crop," he said. "That's an insight we didn't have before.
There was anecdotal evidence, maybe some farmers had noticed a difference, but now we have the science behind why that's really possible and what mechanism allows that to happen." The study is part of Ali and his lab's broader work examining the evolution of how plants defend themselves against pests. He explained that as humans domesticated plants and bred them to grow faster, produce more and taste better, we also unintentionally weakened some of their natural defenses. He compares it to the domestication of wolves into dogs: In selecting for the traits we wanted, we also bred out some of the "fangs" that served a protective purpose.
As a result, growers now need to use strategies such as pesticides and herbicides to protect crops. "What my group has been doing is looking for ways that some of the plants still have the ability—still have some of those metaphorical fangs to fight off pests and disease," Ali said. "If we can put them in the right context, what defenses still remain in our domesticated plants?" Cover cropping has been a popular agricultural practice for thousands of years and has significant effects on soil, plants and insects.
While these benefits are well known, Ali said less was known about how different plants used as cover crops would affect future generations of plants in the same plot of soil. For the study, the researchers planted corn plants in soils conditioned by three cover crops: pea, radish and a wheat-rye hybrid called triticale, along with a control of fallow soil—soil not previously used by a cover crop. They raised fall armyworm larvae, which grow into moths, on the plants in each type of soil.
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