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Biological Control of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (C. maculosa)

Published online by Cambridge University Press:  12 June 2017

Donald M. Maddox
Donald M. Maddox*
Affiliation:
Biol. Control of Weeds Lab., Agric. Res. Serv. U.S. Dep. Agric, 1050 San Pablo Avenue, Albany, GA 94706
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Abstract

Diffuse knapweed (Centaurea diffusa Lam.) and spotted knapweed (C. maculosa Lam.) presently infest approximately 1.5 million ha of pasture and rangeland in Washington, Montana, Idaho, Oregon, and California. The serious losses caused on lands where returns from herbicidal control are marginal or less prompted the testing and introduction of two strains of a seed-head fly (Urophora affinis Frlfld.) as a biological-control agent in these states. Over 27 000 flies were released in about equal numbers on both weeds during the years 1974 to 1977 and in 1979 and 1980. The fly became established in all states where it was released. The adult was found to disperse over 76 m from release point from 1974 to 1976, and to reduce the number of seeds per flower head in sampled heads by 80% in northern Washington and over 64% at the Heppner, Oregon site. A newly released moth (Metzneria paucipunctella Zell.) and a root-boring beetle (Spbenoptera jugoslavica Obenb.) are expected to cause additional pressure on these plants. The reproductive potential of the knapweeds is such that more natural enemies will be needed to provide enough stress to reduce these weedy species to an acceptable level.

Keywords

Natural enemiesseed-head flies
Type
Research Article
Information
Weed Science , Volume 30 , Issue 1 , January 1982 , pp. 76 - 82
Copyright
Copyright © 1982 by the Weed Science Society of America 

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References

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