Spicing up crops may keep pests at bay

Long ago, many plants evolved their own natural pesticides – chemical compounds that repel or kill would-be herbivores. Not quite as long ago, humankind learned to use some of these plants for aromatic, medicinal, and flavor-enhancing purposes. We call them spices.

Now, scientists are looking into using spices and herbs for their evolved purpose – to protect against interlopers on human-cultivated crops. Presenting at the American Chemical Society’s 238th national meeting in Washington, Murray Isman, a professor of agroecology at the University of British Columbia, Vancouver, describes his research into clove, thyme, and mint, among other plants, for possible use as pesticides.

Different herbs and spices have different protective properties. Some kill insects directly, others simply alter their behavior – dissuading females, say, from laying eggs on a plant. Rosemary and thyme have antifungal properties; they protect against powdery mildew. Clove and citrus keep other plants, or weeds, at bay.

The natural pesticides would offer several advantages compared with conventional ones. First, they don’t need to go through the time- and resource-intensive approval process of regulatory agencies.

It’s also possible that insects, which often evolve resistance to conventional pesticides over time, can’t adapt as quickly to these compounds. They’re more complex than human-manufactured pesticides, which hinder pest adaptation, says Isman.

What’s more, the compounds are not toxic to the farmers who apply them. And they can be used in organic-­certified agriculture.

The potential downside of spicy pesticides is that essential oils degrade quickly in sunlight. Using them will probably require more applications than what’s required by conventional pesticides.