Historic, Archive Document Do assume not content reflects current scientific l<nowledge, policies, or practices. . The Problem Leafy spurge (Euphorbia esula L.) has taken over millions of acres of western grazing land. An aggressive, exotic perennial weed, it has greatly reduced the carrying capacity of the range. It Leafy spurge stands cause heavy damage in readily outcompetes desirable native the northern Great Plains. Land managers vegetation. Because of irritating need to take precautions to limit further chemicals in the weed, cattle and spread. horses generally don't graze on and it, Cattle tend to ignore stands of leafy spurge they even avoid nutritious forage grow- because chemicals in the weed irritate their ing nearby. Economic losses may be digestive tract. more than $100 million in the affected States. Herbicides have been used against leafy spurge, but infested acreage is so extensive that chemical control isn't practical. For one thing, herbicides sprayed to kill spurge also kill desirable broad-leaved range plants. Secondly, chemical control is expensive. A 1984 study by the Univer- sity of Wyoming put the cost of apply- ing herbicides at $72 per acre. Costs of spraying outweigh the benefits by as much as 1 0 to 1 Furthermore, the weed is hard to kill with chemicals. It has a pervasive root system and seems to be able to block the downward movement of herbicides. 2 To bypass these difficulties, the U.S. Department of Agriculture (USDA) is coordinating a major biological con- trol program that involves importing and distributing the weed's natural enemies. Biological control specialists in USDA's Animal and Plant Health Inspection Service (APHIS) are concen- trating on insects that have evolved to feed only on the target weed, leafy spurge. Collectively, the feeding insects inhibit the weed's growth and repro- duction and reduce its ability to com- pete with desirable range plants. Spurge infestations can be quite attractive to theeye. Onlywhenitcomestoeconomicsdoes the plant take on an ugly cast. 3 — The Weed A Description Leafy spurge grows in dense clumps with one or more shoots coming from a woody root crown. A milky latex seeps from the plant when it is cut or torn. Its nonwoody, hairless stems, which can reach 3 feet or more in height, hold alternate, usually pointed leaves. In summer, the weed develops a cluster of yellow flowers with large, round, greenish-yellow bracts. Seeds grow inside a three-valved capsule. When the seed is ripe, the capsule bursts, shooting seeds up to 15 feet from the plant. Waterways and Above: The root crown of spurge has animals carry the seed farther. Most of adventitious buds that can sprout readily and the seed germinates the first year, but produce new shoots, adding to the weed's some can germinate up to 7 years later. rapid spread. The roots of spurge, which can Left: Spurge plants can grow to be waist descend 14 feet, help it crowd out high. They bear pointed leaves and a cluster neighboring species and store a large of yellow flowers with large, round, greenish- food reserve. Pink buds on the root yellow bracts. crown sprout readily and produce new shoots, adding to the weed's rapid spread. Today, leafy spurge occupies more The first record of its introduction in than 2.5 million acres. It is concen- North America places leafy spurge at trated most heavily in the northern Newbury, MA, in 1827. By the early Great Plains, particularly in North 1900's, the weed had been carried into Dakota. the Western United States and Canada. 4 A Leafy spurge. Above (A), habit. Top right (B), flower cluster. Bottom right (C), capsule and (D) seeds. Biological Control In Europe and Asia, enough natural from Europe for release in the United inside the plant. The overall effect is to enemies have developed over time to States. Together, these spurge reduce the carbohydrate reserves control leafy spurge without human enemies make a good team for fighting stored in the roots. help. Insects and diseases in the Old leafy spurge because they attack differ- World have put such stress on spurge ent parts of the plant. Some feed on Root-Mining Flea Beetles that it remains an insignificant compo- the leaves. Others attack the shoot Four species of chrysomelid flea nent of the landscape. tips. Still others feed on the stem, the beetles, Aphthona nigriscutis, A. flava, The weed's natural enemies do not root crown, and the deep secondary A. cyparissiae, and A. czwalinae, con- occur in the New World because of its roots. Each attack weakens the plant tribute to the attack on leafy spurge. relatively recent introduction. in a different way, thereby exerting a They were brought to the United States To achieve biological control, human cumulative stress on the weed. from Austria, Hungary, Italy, then- beings needed to intervene. Small Scientists in USDA's Agricultural Yugoslavia, and Canada. numbers of beneficial organisms that Research Service (ARS) are scouting Adults of the four flea beetles live up attack leafy spurge have been released out and evaluating other biological con- to 3 months and feed on the leaves of in North America in the past with lim- trol agents for distribution in North the weed. They lay their eggs on ited success. The critical difference America. Eventually, they hope that spurge stems, about 250 eggs per between earlier efforts and the current there will be enough spurge enemies in female. The larvae cause even more program coordinated by APHIS is one North America to achieve the same damage to spurge, mining the primary of scale. level of control enjoyed in Europe. and secondary roots as well as the fine APHIS' biological control specialists root hairs, thereby disrupting the believe that increasing the numbers of Stem and Root Boring Beetle plant's vascular tissues. beneficial insects released over an The first of the six introduced insects is extensive area will do better than the a cerambyciid long-horned beetle, Shoot-tip Gall Midge modest introductions of the past. The Oberea erythrocephala, which was This cecidomyiid midge, Spurgia project depends on a broad, coordi- brought in from Hungary and Italy. esulae, is a tiny fly imported from Italy. nated effort with cooperation from Females lay an average of 60 eggs and Female adults, which live only 24 to 36 many Federal, State, and industry live between 3 and 8 weeks. hours, lay an average of 73 eggs on the groups. The adult beetle feeds on the out- shoots of leafy spurge. The species can To start with, USDA officials already side of the plant and girdles the stem. produce three to five generations in a have cleared six species of insects The larval stage of the Insect bores into single growing season. the stem and root crown, feeding from 6 ^- Adult flea beetles feed on the leaves of * ~ spurge. Larvae of long-horned beetles bore the stem and root crown. Larvae feed on the shoots and stimulate the plant to form a tumorlike gall on the shoot tips. This gall keeps shoots from forming flowers or seeds and reduces energy reserves of the Adult long-horned beetles from Hungary weed. and Italy girdle the stems of spurge and feed on the leaves. 7 8