Phrydiuchus tau
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Common Name
Mediterranean sage root weevil
Weed Impacted
Larval and adult weevils attack Mediterranean sage. Larval feeding within leaf buds and root crowns can prevent new shoot growth and reduce stem density, ultimately resulting in plant death. Adult beetles cause secondary damage by feeding on rosette (ground-level) leaves. While P. tau can also feed on Clary sage (Salvia sclarea), no nontarget effects have been reported.
Insect Description/Field Identification
Adults are small, brownish-black weevils, 4-5 mm (approximately 3/16 inch) long, with a conspicuous T-shaped mark on the back. Larvae are white, C-shaped grubs found within the root crown.
Life Cycle
Adults emerge in late spring or summer, feed on leaves, then return to the soil to aestivate (summer hibernation-like state) until stimulated once again in the fall. Eggs are laid in the leaf petioles and on the underside of rosette leaves. Larvae hatch and tunnel through leaves into the root crown, where they complete most of their development. Mature larvae exit the plant in the spring and pupate in the soil. Phrydiuchus tau may overwinter in egg, larval, or adult stages (eggs/larvae inside the plant; adults in soil litter outside the plant).
Availability
General availability of these beetles is somewhat limited, although they are readily available locally in some areas of Oregon and Idaho. Eradication of Mediterranean sage is required in Washington, thus all release requests will be assessed on a site by site basis. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
Phrydiuchus tau has successfully controlled Mediterranean sage at sites where perennials are abundant and grazing is limited, but appears to have had little effect in sites with regular disturbance and dominated by annuals.
Using the Agent: Integrated Weed Management (IWM)
Mediterranean sage is currently listed as a Class A Noxious Weed in Washington, so eradication is required and biological control is generally not an appropriate strategy. Releases of P. tau will only be made on a case by case basis.
Smaller populations of the weed can be sprayed and individual plants can be dug out. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Any management of Mediterranean sage should include revegetation with native or other more desirable plants. Revegetation promotes competition between plants, which stresses weeds and may allow for more effective treatment. To learn more about revegetation and IWM, click here.
References
Coombs, E. M., J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. 2004. Biological Control of Invasive Plants in the United States. Western Society of Weed Science, Oregon State Univ. Press, Corvallis.
Photo Credits
Phrydiuchus tau adult - Eric Coombs, Oregon Department of Agriculture
Phrydiuchus tau larvae - L. L. Berry, bugwood.org http://www.insectimages.org/images/768x512/5358624.jpg
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