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Biological control microorganisms for use against invasive annual grasses

The Issue

Invasive plants are detrimental to natural ecosystem services and they reduce biodiversity. Red brome and medusahead are two abundant grass species that are much more invasive here in California than in their Mediterranean countries of origin. This is likely because they left behind their natural enemies, such as root and shoot pathogens, when they left their native habitat. UCCE researchers are trying to understand the effect of above- and below-ground changes in an effort to find a way to control these invasive grasses. Managers and owners of lands affected by the two highly invasive species will benefit from this research.

What Has ANR Done?

Agricultural Experiment Station and UCCE scientists have collaborated with colleagues in Europe to collect plant and soil samples and study how the soil microorganisms foster or discourage the growth of invasive grasses. They examined roots and shoots of red brome and medusahead from sites in Spain and California using growth responses to inoculum from native and invaded soils in growth chambers, and microscopy and DNA sequencing to identify the microorganisms responsible for various growth responses. For red brome, they found a natural enemy in California in the head smut fungus, Ustilago bullata. The same fungus occurs in Spain, and was very likely accidentally introduced to California with brome grasses. Seed pathogens for head smut occurred with as much as 90% frequency in some California stands of red brome. They did not find a pathogen to help control medusahead, but realized that it grows less vigorously in low-nutrient soils. Additional studies with medusahead seeds from European populations are needed to identify potential biological control mechanisms.

The Payoff

Head smut is spreading naturally to control red brome

In this research UCCE scientists are currently culturing head smut and will use it to infect red brome populations in the greenhouse. The eventual goal is to inoculate red brome in the field as a biological control agent. Commercial availability is some years away, but has the potential to provide managers of natural reserves and grasslands a low-cost and environmentally friendly solution to invasive brome grasses.

Clientele Testimonial

“Identification of a biological control would help by providing another tool for control of these invasive grasses, which cause a decrease in habitat quality for EPA-listed and sensitive species. Control of invasive grasses to restore native vegetation and animals is one of the greatest challenges for conservation land managers, and we would welcome a low-cost tool to aide this effort.” - Brian Shomo, Riverside County Habitat Conservation Agency


Supporting Unit: Botany & Plant Sciences

Edith B. Allen, UCCE Specialist and Professor, edith.allen@ucr.edu, 951-827-2123