Biological Control of Yellow Starthistle

Lincoln Smith, USDA-ARS-WRRC, 800 Buchanan St, Albany CA 94710 Joe Balciunas, USDA-ARS-WRRC, 800 Buchanan St, Albany CA 94710 Michael J. Pitcairn, California Dept. of Food and Agriculture, 3288 Meadowview Road, Sacramento, CA 95832

Yellow starthistle ( solstitialis L.) is an alien plant that probably originated from the eastern Mediterranean. It was first collected in California in 1869, and now infests 42% of the state’s townships. It interferes with land use such as grazing and recreation, displaces native species, and is toxic to horses (Sheley, et al. 1999 and papers cited therein).

This weed is much less invasive in its land of origin. This is presumably because natural enemies, such as , plant diseases, or competing plants help to keep it under natural control. We are exploring for insects and pathogens that attack this plant. They are tested for host specificity to make sure they do not attack other plants. After evaluation and approval by state and federal agencies, these agents will be released to try to reestablish the natural control that occurs in the land of origin.

So far, six species of biological control agents have been introduced to control yellow starthistle (Turner et al. 1995; Rees et al. 1996; Jette, et al. 1999). All six attack the seedheads. The most promising agent is the hairy weevil (Eustenopus villosus), which is well established in California and occurs in high densities, attacking 25 to 80% of seedheads. Adults damage young flower buds by feeding on them, and lay eggs on later-developing flower buds. Their larvae develop inside a seedhead and consume all the seeds. However, this insect has only one generation per year and does not attack flowers that develop later in the summer. The other established agents, sirunaseva, Bangasternus orientalis, australis and curtus are fairly widespread (see Table) but do not attain high numbers and appear to have little impact on yellow starthistle populations. is better synchronized with bachelor button, which blooms earlier in the spring than yellow starthistle. Bangasternus orientalis appears to suffer from high egg predation and parasitism. The gall , Urophora jaculata, failed to establish because yellow starthistle in California is unsuitable for the fly (Clement 1994). The fly originated from a population of yellow starthistle in Italy that was much more susceptible to its attack. Recently, the parasitic mite Pymotes tritici has been found attacking seedhead insects in California and may be reducing their effectiveness.

The false peacock fly (), which was accidentally introduced in 1991, emerges in the spring about a month before the plant has developed flower buds large enough for egg-laying. However, the fly has several generations per year and increases numbers progressively through the growing season, complementing the seasonal activity of the hairy weevil. The false peacock fly is being tested for nontarget impact on and native thistles and preliminary results have shown no significant adverse effects.

The rust pathogen, Puccinia jaceae, has been evaluated for host specificity by William Bruckart at the USDA-ARS laboratory in Fort Detrick, MD. A petition for its introduction has

2001 Proceedings of the California Weed Science Society (Volume 53) 105 recently been submitted. Foreign exploration and evaluation of additional agents is currently increasing in , Russia, and Italy.

Status of yellow starthistle biological control agents

Biological control First agent Common name release Status Urophora jaculata 1969 Never established in USA.

Urophora sirunaseva YST1 gall fly 1984 Widely established, present at most YST infestations in CA & OR; a few sites in WA, ID. Bangasternus orientalis YST bud weevil 1985 Widespread in CA, OR, WA & ID.

Chaetorellia australis YST peacock fly 1988 Prefers bachelor button; established at a few sites in CA; widespread in OR, WA, ID. Eustenopus villosus YST hairy weevil 1990 Well established in CA; widespread in OR, WA; a few sites in ID, UT. Larinus curtus YST flower weevil 1992 Established at a few sites in CA, WA, ID; widespread in OR. Unapproved accidental introduction: Chaetorellia succinea YST false peacock 1991 Widely established in CA & OR, and spreading into fly WA, ID & NV. Currently being evaluated for nontarget impacts. 1 YST = yellow starthistle

References

Clement, S. L. 1994. Resistence among populations of yellow starthistle to thistle-head insects: Results from garden plots in Italy. Biol. Contr. 4: 149-156.

Jette, C., J. Connett and J. P. McCaffrey. 1999. Biology and Biological Control Agents of Yellow Starthistle. United States Department of Agriculture, Forest Service. FHTET-98-17.

Rees, N. E., P. C. Quimby, G. L. Piper, E. M. Coomb, C. E. Turner, N. R. Spencer and L. V. Knutson (eds.). 1996. Biological Control of Weeds in the West. Western Society of Weed Science., USDA-ARS, Montana State University, Bozeman, MT. World Color Printers, Bozeman, MT.

Sheley, R. L., L. L. Larson and J. J. Jacobs. 1999. Yellow starthistle, pp. 408-416. In, Sheley, R. L. & J. K. Petroff, eds., Biology and Management of Noxious Rangeland Weeds. Oregon State University Press, Corvallis.

Shishkoff, N.; W. L. Bruckart. 1996. Water stress and damage caused by Puccinia jaceae on two Centaurea species. Biological control: theory and applications in pest management 6(1): 57.

Turner, C. E., J. B. Johnson and J. P. McCaffrey. 1995. Yellow starthistle, pp. 270-275. In J.R. Nechols, L.A. Andres, J.W. Beardsley, R.D. Goeden and C.G. Jackson (editors), Biological Control in the Western United States: Accomplishments and Benefits of Regional Research Project W-84, 1964- 1989. University of California, Division of Agriculture and Natural Resources, Oakland. Publ. 3361.

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