Wanted: A Few Good Microbes

Problem: How to reduce usage of chemical pesticides. Solution: Develop natural products based on killer bacteria.

Pamela Marrone had her first professional epiphany at age 9 when her father tried to save a prized dogwood tree from gypsy moths by spraying it with a chemical pesticide. “Afterward, everything on that tree–including all the ladybugs and honeybees–lay dead on the ground,” she says. It was a catalytic event: Marrone went on to earn a PhD in entomology and dedicate her career to finding safer ways to control plant diseases.


Her 8-year-old company, AgraQuest, has set the industry standard for commercializing natural fungicides and pesticides, bacteria with the power to kill fungi and molds. Unlike chemical sprays derived from gasoline and crude oil, biopesticides are water soluble, ephemeral, and nontoxic to larger life forms.

The search for a few good microbes has taken Marrone and her team from the Honduran rainforest to the dry creekbeds of northern California. AgraQuest’s first product, Serenade, a fungicide that treats rots and mildews on grapes and other fruits and vegetables, is based on a microbe named Bacillus subtilis, discovered when a local Fresno County peach grower noticed some of his trees never seemed to become infected with brown rot. Marrone’s crew swabbed the trees and their fruit, and then cultured their finds in petri dishes. “This one microbe was creating a huge zone of inhibition–nothing was growing near it,” Marrone says. From that, AgraQuest created a product that could compete with its chemical brethren.

Persuading farmers to try it has been a challenge. But Serenade has been licensed for use in Chile, Costa Rica, Honduras, Japan, Mexico, New Zealand, and the United States. In Costa Rica, a major banana grower has cut its use of Dithane–a notorious environmental pollutant and carcinogen–by half, simply by mixing the pesticide with Serenade.

Agraquest, which is privately held, has yet to turn a profit. But the company just won Environmental Protection Agency approval for a new product called Rhapsody, and has three more–a fungicide, an insecticide, and a fumigant–under EPA review. And there are countless bacteria out there, just waiting to be commercially exploited.