15 CYPRESS SPURGE PEST STATUS of WEED Nature Of
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15 CYPRESS SPURGE H. Faubert and R. A. Casagrande Department of Plant Sciences, University of Rhode Island, Kingston, Rhode Island, USA become a major weed in other areas. In 1975, it was PEST STATUS OF WEED found in 26 states; 25 years later it was recorded in 42 Cypress spurge (Euphorbia cyparissias L.) (Fig. 1) is states (Dunn, 1979; USDA, NRCS, 1999). At one site a herbaceous European perennial introduced into in Rhode Island, approximately 70 out of 170 acres North America as an ornamental plant in the 1860s of hay meadow were dominated by cypress spurge, (Croizat, 1945). It was widely planted in graveyards making most of the land unfit for cattle and growing and often is called graveyard weed (Muenscher, 1936). hay. Farmers who are unaware of cypress spurge in The plant escaped cultivation and became established their hay fields spread the weed when transporting on open ground, particularly in pastures (Stuckey and hay infested with cypress spurge seeds. Chemical Pearson, 1973). control of cypress spurge is difficult because of its extensive root system. Plants readily regrow from roots following destruction of above-ground parts, so repeated applications of several herbicides usually are required for control (Pemberton, 1985). Culti- vating infested fields can spread cypress spurge by moving root pieces caught on machinery to clean lo- cations where roots produce new plants (Moore and Lindsay, 1953). All parts of cypress spurge contain a toxic latex (Stephens, 1980) that irritates the eyes, mouth, and gastrointestinal tract and causes dermatitis upon con- tact in some people (Westbrooks and Preacher, 1986). Most grazing animals avoid cypress spurge. Sheep can Figure 1. Euphorbia cyparissias L. in bloom. (Photograph by R. A. Casagrande.) browse the plant with no ill effects, but cattle that accidentally ingest it become weak, collapse, and may Nature of Damage die (Muenscher, 1964). Ecological damage. Cypress spurge is primarily Economic damage. Although cypress spurge is found found on limestone, sandy, or gravelly soils. It tends throughout much of North America, economic losses to form almost pure stands at open sites and is likely are primarily restricted to the northeastern United to be responsible for displacement of native species States (USDA, NRCS, 1999; Stahevitch et al., 1988). (Moore and Lindsay, 1953; Stuckey and Pearson, Cypress spurge is particularly prevalent in Ontario 1973). Cypress spurge does not generally occur on and Quebec (Gassmann, 1985). In the United States, intensively cultivated soils, nor is it found in heavily 25 counties have infestations of more than 500 acres forested areas (Stahevitch et al., 1988). This weed is and most of these sites are in the northeast (Dunn, commonly found along roadsides throughout the 1979). Cypress spurge is listed as a noxious weed in northeastern United States, but generally is not con- Canada and some New England states (Stahevitch et sidered a problem as it forms an attractive ground al., 1988; Torrey, 1999) and it has the potential to cover. 195 Biological Control of Invasive Plants in the Eastern United States Geographical Distribution BACKGROUND INFORMATION Native to Europe, cypress spurge is found through- ON PEST PLANT out the continent between 40 and 60 ºN (Pritchard, 1959). In North America, it is currently found in 42 Taxonomy states and Canada (Dunn, 1979; USDA, NRCS, Cypress spurge is a member of the Euphorbiaceae, 1999). It also is an invasive weed in New Zealand or spurge family. Synonyms for E. cyparissias are (Stahevitch et al., 1988). There are three cytogenetic Galarhoeus cyparissias (L.) Small and Tithymalus variants present in Europe – fertile tetraploids (Fig. cyparissias (L.) Hill. The genus Euphorbia contains 2), fertile diploids, and sterile diploids. Fertile about 1,600 species native to Africa, Asia, Europe, tetraploids, the most widely distributed form, are and North America (Gassmann et al., 1991). In found throughout the range from southern Finland North America, native or introduced species are to northern Greece and west from England to as far found in four subgenera: Agaloma, Chamaesyce, east as Lake Baikal in central Siberia (Pritchard, 1959). Esula, and Poinsettia (Pemberton, 1984). Cypress Fertile diploids have a relatively southern distribu- spurge and the closely related leafy spurge, Euphor- tion (France, Italy, Switzerland, Austria, and the bia esulae L., belong to subgenus Esula (Gleason and former Yugoslavia), while sterile diploids are found Cronquist, 1991). Leafy spurge is another invasive primarily in England (Pritchard, 1959). Only sterile Eurasian species that has caused considerable dam- diploids and fertile tetraploids are found in North age in the north central United States and the Cana- America (Stahevitch et al., 1988). The sterile diploid dian prairies (Gassmann, 1985). Euphorbiaceae typi- was probably intentionally introduced as an orna- cally have a poisonous white sap in all plant parts mental plant in North America and the fertile tetrap- (Clark and Fletcher, 1909), which appears to be for loid was apparently accidentally introduced. The tet- defensive purposes (Gassmann et al., 1991). raploid form is considerably more vigorous and weedy than the diploid form (Dunn, 1979; Gassmann Native Range and Schroeder, 1995), and this form has been increas- ing in abundance in North America. Reports of fruit- According to Stahevitch et al. (1988), cypress spurge ing cypress spurge (fertile tetraploid) were rare in is found throughout Europe from 60 ºN in southern North America from 1910 to 1931, but became more Finland to 40 ºN is northern Greece, and ranges from common by 1953 (Deane, 1910; Deane, 1912; Britain to central Siberia. Muenscher, 1931; Moore and Lindsay, 1953). In Biology Rhode Island during the spring of 2000, we conducted a survey in 54 cypress spurge stands. Fifty-three out Cypress spurge is a perennial that overwinters as root of the 54 stands were comprised of fruiting plants, and crown tissue. The fertile tetraploid also can over- indicating a predominance of tetraploid cypress winter as seed. The root system consists of two root spurge in the state. types. Young seedlings send out a taproot that is persistent and indeterminate. The taproot may reach lengths of three or more meters and give rise to lat- eral roots, which produce adventitious buds. In early spring, shoots develop from the crown and buds. Shoots grow in masses and reach about 40 cm in height before flowering in mid-spring. The sterile diploid cypress spurge flowers but does not set seed. The fruit of the fertile form is an explosive capsule that splits open when mature and throws its seed up to five meters (Stahevitch et al., 1988) Analysis of Related Native Plants in the Eastern United States Figure 2. Close-up of fruiting structure of tetraploid Euphorbia cyparissias L. There are 107 Euphorbia species native to North (Photograph by R. A. Casagrande.) America, 21 of which are in the subgenus Esula 196 Cypress Spurge (Pemberton, 1985). In the northeastern United States plex of specialized insects and pathogens (Spencer, there are 13 native Euphorbia species, of which three 1994). Leafy Spurge has been the target of a biologi- are in the subgenus Esula: Euphorbia commutata cal control program since 1961. Because cypress Engelm., Euphorbia purpurea (Raf.) Fern., and Eu- spurge is closely related to leafy spurge, agents re- phorbia spatulata Lam. (USDA, NRCS, 1999; Magee leased against leafy spurge also were released against and Ahles, 1999) (Table 1). Euphorbia purpurea is cypress spurge. listed as a species of concern by the U.S. Fish and Leafy spurge probably originated in northern Wildlife Service and is under review for protective Caucasus or northern China (Kuzmanov, 1964). status. This plant is found in swampy woods in the However, because of political and financial limita- eastern United States (Pemberton, 1985). The other tions, surveys were conducted in the most western native Euphorbia species are in one of three other part of its distribution in Europe. Surveys originally subgenera found in North America: Agaloma, funded by Canada began in 1961 at the International Chamaesyce, or Poinsettia (Gleason and Cronquist, Institute of Biological Control of the Centre for Ag- 1991). In addition to cypress and leafy spurge, ten riculture and Biosciences International (CABI-IIBC) other Euphorbia species in the subgenus Esula have in Delemont, Switzerland (Gassmann, 1990). Insects been introduced into the Northeast (USDA, NRCS were collected from leafy spurge and cypress spurge 1999). Subgenera appear to be natural groupings. plants in Italy, Switzerland, Germany, Austria, Hun- Many Euphorbia-feeding insects accept as host plants gary, and the former Yugoslavia. From 1980 to 1990 most of the species in one subgenus and reject spe- field surveys were expanded in scope to include other cies in the other subgenera (Pemberton, 1985). common perennial spurges in the subgenus Esula. This was done to enlarge the range of plant habitats from very dry to moist. In particular, Euphorbia BACKGROUND INFORMATION seguieriana Necker and Euphorbia lucida Waldstein ON PEST PLANT and Kitaibel were included in the survey. Field sur- veys were terminated in 1990 (Gassmann and Area of Origin of the Weed Schroeder, 1995). Cypress spurge is believed to be indigenous to west- Natural Enemies Found ern Europe where the fertile diploid form of the plant is found. Fertile diploids occur throughout France Thirty-nine insect species and two rust fungi were and northcentral Spain and also in a narrow band found and considered for the biological control of across central Europe (excluding the Alps). Fertile leafy spurge and 22 of the insects were screened as tetraploids probably arose from fertile diploids, en- potential control agents. Originally, the selection was abling the plant to colonize new habitats. Tetraploids based mainly on agent availability and the damage a apparently replaced diploids in most locations and single individual caused to plants. This led to a focus extended the range of the species to the north and on species with large individuals, like the sphingid east.