Transportation Research Record 805 l Biological Control of Carduus Thistles Along Roadsides in Northeastern States SUZANNE W.T. BATRA The host·specific European seed-destroying weevil, Rhinocyllus conicus, Bull thistle (Cirsium vulgare) is the predominant has been released at 72 sites in Maryland and Pennsylvania for the bio· thistle in the coastal eastern region (zones l and logical control of Carduus thistles in crown vetch. Established popula· 2) on the red clay or sandy soils; Carduus thistles tions along roadsides are spreading into adjacent thistle-infested pastures. occupy the same ecological niche in zone 3 (lime­ Another host-specific European beetle, Trichosirocalus horridus, which stone soils), and Canada thistle (Cirsium arvense) attacks rosettes, will be released along roadsides in 1981. becomes predominant in western Maryland · as well as in other areas north and west of the Great valley. The distribution of c. acanthoides and c. nutans The northeastern region includes West Virginia, is positively correlated with the. location of fer­ Maryland, Pennsylvania, New York, Delaware, New tile soils developed over limestone in three con­ Jersey, and the six New England States. Carduus tiguous counties, Franklin (Pennsylvania) and Fred­ species occurring in this region are c. acanthoides erick and Washington (Maryland). In Franklin County (plumeless thistle), C. crispus (curled or welted (_1), this valley soil, referred to as the Hagers­ thistle), and c. nutans and c. thoermeri (nodding or town-Duffield association, occupies 32 percent of musk thistle) • the county, where nearly all is cleared for crops, Carduus crispus is an economic problem only in orchards, hay, and pasture. Carduus thistles in West Virginia, where the host-specific European Franklin County also extend their range to somewhat weevil Rhinocyllus conicus has been established by overlap adjacent areas of thicker valley soils the West Virginia Department of Agriculture in overly1ng limestone (Murrill-Laiding formation) or Monroe County for its control <ll· This thistle has shale and sandstone (Weikert-Becks-Bedington asso­ been present in the general area since about 1920 ciation). The reddish to yellowish soils of the Cl>· Hagerstown-Duffield-Frankston association occupy 46 Carduus nutans was first recorded in the United percent of the total area of Washington County, States in 1853 at Harrisburg, Pennsylvania C]), Maryland. Although cultivation may be hindered by where musk thistle still remains a serious pest. the numerous limestone ledge outcrops, this most Other early northeastern introductions were in fertile soil ii).> the county provides high yields in ballast dumped at Hoboken (1893) and Camden, New corn, small grains, hay, and pasture (6). About 10 Jersey (1880); at Providence harbor, Rhode Island percent of Frederick County is occ;pied by the (1890); and at Washington, D.C. (1897). Carduus well-drained Duffield-Hagerstown-Sasquatchie-Athol acanthoides similarly appeared first at ballast valley soils developed from limestone and shale over dumps at Camden (1878) and Hoboken (1880), and at limestone rocks much less acidic than surrounding Providence harbor (1893); it was found in Ohio in areas <ll. Although there may be massive outcrops 1878. of hard limestone, excellent yields support numerous Carduus nutans, c. thoermeri and c. acanthoides farms and productive dairying. Although Carduus is in the northeast often occupy the same habitats, most prevalent on these soils, some thistles grow in such as overgrazed pastures and roadsides, sometimes adjacent poorer micaschist-derived soils of the occurring as mixed stands. These plants are trou­ Piedmont plateau where underlaid by marble or lime­ blesome primarily in the Great Valley region, which stone. These plants are rarely found to the west or is a northeastward extension of the Shenandoah north on stony, steep mountain soils or on the Valley of Virginia and located between two long, shallow soils of red shale and sandstone in the parallel mountain ridges. Serious infestations are valleys. As may be seen from the above data, found from northern West Virginia to near Hagerstown Carduus thistles are a particularly serious economic and Frederick, Maryland, to Harrisburg, and eastward pest because they interfere with agriculture on the past Allentown, Pennsylvania, into western New most productive soils of the region. Jersey. As noted in Ohio by Stuckey and Forsyth (3) The geographic distribution of economic infesta­ and in Virginia by Hensley (_!), these thistles in tions of Carduus thistles in the northeast appears the northeast create economic infestations primarily to be long-standing and related to the availability when growing in shallow soil over limestone. Scat­ of soils formed over limestone. This does not seem tered plants or patches may be found elsewhere and, to be the case with the recent and rapidly spreading due to their conspicuousness, these may be rela­ infestations occurring in the central Midwestern and tively well represented in herbaria. However, the Mountain States in various soils (8-10). According early introductions outside the limestone zone to Doing and others (11) , c. nutans in Australia apparently did not create major infestations there. grows in moist, neutral, well-drained soils over For example, as one progresses from east to west basalt or granite; fertile and calcareous soils are across Maryland, four zones are encountered: rare in climatic zones suitable for this plant. An introduced European weevil, Rhinocyllus 1. Eastern shore (Delmarva Peninsula)--sandy conicus, was released on C. nutans, C. acanthoides, soils, and c. thoermeri in Maryland and Pennsylvania in 2. Piedmont plateau (area around Washington, 1975 at 10 sites, in 1976 at 19 sites, in 1977 at 9 D.C.)--primarily poor red clay or mica-schist soils, sites, in 1978 at 12 sites, in 1979 at 7 sites, and 3. Great Valley--well-drained fertile soils in 1980 at 15 sites. These releases of R. conicus developed over limestone, and were made in heavily infested pastures, in vacant 4. Western Maryland beyond Hancock--shale, sand­ land, and also along highways where Carduus thistles stone, or schist. have crowded out crown vetch (Coronilla varia) planted on steep banks for erosion control. The beetles were collected at White Hall, Frederick 2 Transportation Research Record 805 County, Virginia, and released during the above Report Vol. 25, No. 30, 1975, p.625. years at sites in the following counties: Prince 2. M.F. Johnson. Cynareae (Asteraceae) in Vir­ George's, Frederick, Washington, and Baltimore in ginia: Cirsium, Carduus, Onopordium. Virginia Maryland and York, Cumberland, Franklin, Lancaster, Journal of Science, Vol. 25, 1974, pp. 152-160. Berks, Centre, and Dauphin in Pennsylvania. As a 3. R.L. Stuckey and J.L. Forsyth. Distribution of result, populations have become established since Naturalized Carduus nutans (Compositae) Mapped - 1978 and are spreading of c. nutans of 7 of 11 in Relation to Geology in Northwestern Ohio. - locations checked in 1979: Beltsville, Maryland Ohio Journal of Science, Vol. 71, No. 1, 1971, (100 percent plants infested): junction of I-70 and pp. 1-15. Appalachian Trail, Maryland (50 percent plants 4. M.S. Hensley. Taxonomy and Distribution of infested): Fort Detrick, Maryland (9 percent infes­ Cirsium and Carduus Thistles in Rockingham tation): Pinola, Pennsylvania (10 percent infesta­ County, Virginia. Virginia Journal of Science, tion): 1-81 at Greencastle, Pennsylvania (93 percent Vol. 24, Nn. 3, 1973, p. 140. infestation): at Scotland, Pennsylvania (30 percent 5. R.S. Long. Soil Survey Franklin Co., Pennsyl­ infestation): and at Shippensburg, Pennsylvania (75 vania. U.S. Soil Conservation Service, Washing­ percent infestation): and of c. acanthoides at State ton, DC, 1975, 123 pp. College, Pennsylvania. This insect has proven 6. E.D. Matthews. Soil Survey Washington County, effective in controlling Carduus nutans in other Maryland. U.S. Soil Conservation Service, regions (12,13). Washington, DC, Series 1959, No. 17, 1962, 136 In the northeast, it has also been released in pp. Hunterdon, Warren, and Burlington Counties, New 7. E.D. Matthews. Soil Survey Frederick County, Jersey, and Monroe, Jefferson, Berkeley, Pendleton, Maryland. U.S. Soil Conservation Service, Grant, and Hardy Counties, .west Virginia (!,,14). Washington, DC, Series 1956, No. 15, 1960, 144 The spread and impact of these first population pp. establishments along roadsides in the northeastern 8. M.K. McCarty. New and Problem Weeds, Musk states will continue to be evaluated: and new re­ Thistle. Proc., North Central Weed Control leases of R. conicus will be made as needed. Conference, Vol. 20, 1964, pp. 62-63. Cassida rubiginosa, an accidentally introduced 9. M.K. McCarty, C.J. Scifres, and L.R. Robison. A chrysomelid beetle, is abundant on C. nu tans and c. Descriptive Guide for Major Nebraska Thistles. acanthoides in Maryland and Pennsylvania. This Univ. of Nebraska Agricultural Experiment Sta­ defoliator, which also attacks Canada thistle, tion, Publ. SB 493, 1973, 23 pp. Cirsium arvense (~),does not seem to significantly 10. P.H. Dunn. Distribution of Carduus nutans, C. reduce the vigor of Carduus thistles, although acanthoides, C. pycnocephalus, and .c. crispus in leaves may be extensively damaged in some areas. the United States. Weed Science, Vol. 24, No. A newly imported European thistle rosette-de­ 5, 1976, pp. 518-524. stroying weevil, Trichosirocalus horrid us, will be 11. H. Doing, E.F. Biddiscombe,