JOURNAL OF PESTICIDE REFORM/ SPRING 1998 • VOL.18, NO. 1

● NONCHEMICAL MANAGEMENT OF NOXIOUS WEEDS LESSONS FROM LEAFY SPURGE AND YELLOW STARTHISTLE

Noxious weeds are non-native plants, mostly weeds of rangeland or pasture, that are classified under federal and state law as having negative impacts on agriculture. In many states, counties, and cities, control of noxious weeds is mandated by law.

Leafy spurge and yellow starthistle are examples of noxious weeds that are widespread in the Pacific Northwest. Both species are commonly found in disturbed areas, have characteristics that make them successful weeds, and have been difficult to manage with herbicides. For both of these weeds nonchemical management techniques are successful, including mowing, grazing, burning, mulching, seeding of desirable plants, and introduction of biological control agents.

What can leafy spurge and yellow starthistle teach us about management of noxious weeds in general? Seven important lessons emerge: 1) Noxious weeds have been with us for decades, and there is time to develop successful and sustainable management strategies; 2) A focus on eliminating the causes of weed problems is imperative, so that we create long-term solutions; 3) Biological control is a useful and cost-effective technique; 4) Management techniques need to include tools to reduce seed populations; 5) Encouragement of desirable vegetation is crucial; 6) Proper timing can maximize the effectiveness of nonchemical controls; and 7) Techniques must be appropriate for the treatment site.

Leafy Spurge BY CAROLINE COX Leafy spurge (Euphorbia esula) is a pe- rennial weed whose milky sap is toxic to WHAT IS A Many of us have heard the nega- cattle, causing skin irritation and diges- tive rhetoric that is often used in refer- tive problems.2 It is widespread on mil- NOXIOUS ence to noxious weeds. Their encroach- lions of acres in the western United States ment is reaching “epidemic proportions”1; and Canada,2 and estimates of economic WEED? they are “alien, exotic, and invading”1; losses are over 140 million dollars.3 their spread is “rendering wetlands and Spurge is not native to North America; As defined by federal law, nox- habitat unusable by wildlife”1; and they its native range is Eurasian, from Siberia ious weeds are weeds that are “of represent a “catastrophic shift toward southwest to the Mediterranean and west foreign origin”1 and “new or not weedy vegetation.”1 Most of us have also to northern Europe. It was introduced to widely prevalent in the United heard this kind of language used as a jus- North America over a hundred and fifty States”1 when such weeds “can di- tification for herbicide spray programs on years ago, most likely as a contaminant rectly or indirectly injure crops, hundreds or thousands of acres. in soil used as ballast in ships and in im- other useful plants, livestock, or This article presents a different per- ported seed grains.4 The oldest preserved poultry or other interests of agri- spective on noxious weeds. Two case stud- specimen of spurge was collected in Mas- culture.”1 The phrase “interests of ies of noxious weeds, leafy spurge and sachusetts in 1827.2 agriculture” is defined to also in- yellow starthistle, show that nonchemical Several physical characteristics make clude irrigation, navigation, or fish techniques can successfully manage weeds, spurge a tenacious weed. It has an exten- and wildlife resources.1 and have done so throughout the North- sive root system, and average-sized plants Many states designate weeds as west. Then, from these two examples, (2 feet tall) can have roots that extend 10 noxious, and both state and local NCAP draws some general conclusions feet into the soil.2 These roots crowd out governments commonly have laws that can be used in evaluating manage- neighboring plants and also store food, that require landowners to control ment programs for any noxious weed. enabling the plant to survive unfavorable noxious weeds that grow on their conditions. In addition, buds on the roots property. 2 can sprout and produce new shoots, and 7 U.S.C. 61 § 2802. Caroline Cox is JPR’s editor. a root fragment as small as 2 inches can

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spurge, the most promising natural en- emies are the leafy spurge flea beetles. One beetle, Aphthona nigriscutis, has given “excellent control”10 in areas with lighter soils. In Alberta, Canada, leafy spurge was reduced 99 percent five years after release of the beetle.10 In Manitoba, spurge was reduced 93 percent 7 years after release.11 In Fremont County, Wyoming, over 50,000 square feet of leafy spurge was eliminated in the first four years after re- lease.12 On a Montana ranch, beetles pro- vided 80 percent control of spurge over an area three miles long and a mile wide in six years.9 A related species Aphthona cyparissiae, which prefers moister soils, has also been widely distributed. Researchers believe that these flea beetles “should solve the prairie leafy spurge problem on dry, light, open soils.”11 What is needed now are similarly effective natural enemies on Aphthona flea beetles on leafy spurge. The beetles have been introduced as biological control agents wetter, heavier soils. Another related flea of leafy spurge and have effectively reduced spurge populations on light well-drained soils. beetle, Aphthona czwalinae, has the po- tential to meet this need.13 produce a mature plant in one season.2 lars trying to control spurge on a 700 Another nonchemical tool that has suc- Spurge seeds grow inside a capsule that acre ranch7 that had been overgrazed by cessfully managed spurge is grazing by bursts when the seed is ripe, dispersing its previous owners.8 His evaluation of sheep and goats. Unlike cattle and horses, seeds up to 15 feet.5 The seeds can live the efficacy of the herbicides? “The chemi- sheep and goats like spurge, particularly for up to 7 years in the soil,5 so that cals were a joke.”7 In central Montana, after they become accustomed to the germination of new seedlings can occur rancher Tom Elliot spent two seasons and weed. On experimental plots in Canada, long after visible plants are gone. over 25,000 dollars trying to control 5 years of sheep grazing reduced the Leafy spurge is primarily, although not spurge with chemicals. The result? “You amount of spurge 93 percent. Successful exclusively, found in disturbed areas. A would have thought we put fertilizer on grazing of spurge requires starting early study of a native prairie found that 95 the stuff,”9 he reported. in the season because sheep prefer small percent of the spurge plants were associ- The picture painted here is clearly one spurge plants.14 Sheep grazing of spurge ated with soil disturbances. Seedling es- of a difficult weed. Yet, nonchemical tech- provides income for ranchers because they tablishment was 45 times greater on bare niques for managing leafy spurge are both can lease their range to sheep producers.9 soil than in undisturbed vegetation.6 available and effective. Grazing by angora goats is also a suc- Chemical control of spurge has been One management tool is biological cessful management tool. In North Da- problematic. Herbicides that kill leafy control, the importation and distribution kota, 3 years of grazing by angora goats spurge also kill desirable plants. Also, her- of the weed’s natural enemies. In spurge’s resulted in a decrease in leafy spurge bio- bicide costs can easily exceed the value of native areas it is of little or no economic mass of 44 percent, and an increase in the land on which they are used. The significance.2 According to USDA, “in- grass biomass of 57 percent.15 Angora U.S. Department of Agriculture has esti- sects and diseases in the Old World have goats have also been used on infested mated that the costs of spraying outweigh put such stress on spurge that it remains range in Oregon and Idaho.7,16 These the benefits by as much as 10 to 1.5 an insignificant component of the land- projects are new, with only one season of In addition, spurge is hard to kill with scape.”5 The insects and diseases were not grazing, but results so far are promising.8 herbicides because the plant is able to introduced to North America along with Seed production was completely elimi- block movement of the chemicals to the the weed.5 Biological control involves nated in the Oregon project.17 root system, allowing the roots to survive bringing these natural enemies to North Along roadsides, planting of competi- herbicide treatment.5 For example, Rich American spurge infestations. tive grasses, including the native grass Sacchi, a rancher in south-central Oregon, Although a number of different insects little bluestem, has successfully reduced spent four years and over 100,000 dol- have been introduced to manage leafy spurge abundance. In an experiment

NORTHWEST COALITION FOR ALTERNATIVES TO PESTICIDES/NCAP P.O. BOX 1393, EUGENE, OREGON 97440 / (541)344-5044 3 JOURNAL OF PESTICIDE REFORM/ SPRING 1998 • VOL.18, NO. 1 funded by the Minnesota Department of years ago as a contaminant in alfalfa seed Transportation, spurge declined 67 per- brought to California from Spain and Figure 2 cent two years after grass seeding.18 Chile. The oldest preserved specimens Yellow Starthistle Abundance Is Reduced by Yellow Starthistle were collected in 1897. Efforts to control Mowing and Seeding Clover this weed were begun in 1917.22 Yellow starthistle (Centaurea solstitialis) Three attributes of yellow starthistle 500 is an annual weed, one that completes its make it a successful weed. First, its long life cycle in a single growing season. Seeds tap root allows it to use water deep in germinate anytime between October and the soil and gives the plants a high toler- June, depending on when rain occurs.19 ance for drought. Second, patches of seed- The plant then grows as a rosette with a lings are often dense, and block sunlight robust tap root that can reach a depth of from reaching the soil surface. This sup- 400 6 feet by early summer. In May or June, presses the growth of other species.19 Fi- the plant bolts, then flowers, and sets nally, starthistle plants produce an ex- seed.20 traordinary amount of seed. Each plant produces between 700 and 10,000 seeds;20 an acre of starthistle will produce between 50 and 200 million seeds.19 While most seeds are short-lived, some 300 persist in the soil for up to 10 years.23 Starthistle thrives in areas where other vegetation has been disturbed by fire, con- struction, or overgrazing. For example, in an experiment at Washington State University, artificial cattle grazing (clip- 200 ping that simulates grazing) reduced the ability of four perennial grasses to resist invasion by yellow starthistle.24 Management of yellow starthistle with herbicides “is not ideal and often results 25 in failure,” according to a researcher 100

from the University of California at Seedling density after three years of treatment (number per square meter) Davis’s Weed Science Program. Many herbicides that control starthistle also in- jure desirable grasses. Several combina- tions of herbicides provide only moder- ate control. Often multiple applications 0 are required because seed germination The weevil Eustenopus villosus has been in- 21 Untreated Mowed Seeded with troduced in the pacific Northwest to reduce occurs over a long period. Resistance to clover, then yellow starthistle populations. multiple herbicides has been documented mowed in yellow starthistle populations that have Source: Thomsen, C.D., M. P. Vayssieres, Starthistle is toxic to horses and causes been frequently treated with herbicides.26 and W.A. Williams. 1997. Mowing and 20 subclover plantings suppress yellow a fatal nervous system disease. Mature Overall, yellow starthistle is clearly a starthistle. Calif. Agricul. (Nov.-Dec.):15-20. plants are unpalatable to cattle because weed that is difficult to manage. Yet, as of their spiny flower heads.21 with leafy spurge, nonchemical techniques Starthistle is widespread throughout In field experiments, mowing of yellow starthistle for managing this weed are both avail- combined with seeding of clover reduced yellow the Pacific Northwest. It occupies 10 mil- able and effective. starthistle populations by over 99 percent. lion acres in California,19 980,000 acres One successful nonchemical technique in Oregon, 200,000 acres in Idaho, and for managing starthistle is grazing by settes, starthistle thrives. With appropri- 130,000 acres in Washington.21 sheep or goats. To be successful, grazing ate timing, however, grazing is highly ef- Like spurge, yellow starthistle is not must occur during bolting, and then be fective. In one set of experiments in Cali- native to North America. It was intro- continued to remove any regrowth. If fornia, grazing reduced the number of duced into California over a hundred plants are only grazed when they are ro- flower heads up to 90 percent.27

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Mowing is also an effective villosus. Eustenopus has more impact on ious weeds. Like leafy spurge and yellow nonchemical tool. Again, timing is cru- starthistle than the other insects because starthistle, many noxious weeds were in- cial. Early mowings can increase starthistle both larvae and adults feed on develop- troduced into North America over a hun- density, probably because it suppresses ing flower heads.30 Near Myrtle Creek, dred years ago and have been here since. competing vegetation. However, mowing Oregon, densities of yellow starthistle Although infestations are often portrayed when plants had just started to bloom were “greatly reduced”31 following intro- as crises, there is always time to develop reduced subsequent flower head density duction of the weevil, combined with a successful, sustainable strategies. between 63 and 86 percent. Seedling den- reduction of cattle grazing and increases The only time quick action is manda- sity the following fall was reduced be- in competition from perennial grasses.31 tory is when a small population of a newly tween 73 and 89 percent.27 On small sites, other nonchemical introduced weed is found. In this situa- When a second mowing removed re- techniques can be useful. Straw mulch tion simply pulling the undesirable plants growth, starthistle densities were reduced provides good control of starthistle, with is the appropriate response. even further. Density of flower heads was a 3.5 inch mulch yielding 98 percent con- reduced up to 97 percent, while densities 2. Identify and Eliminate the of seedlings the following fall was reduced Causes of Weed Problems up to 98 percent.27 When these treat- “ Attempts to control Like leafy spurge and yellow starthistle, ments were repeated for three years, the most noxious weeds thrive in disturbed results were especially striking: seedling weeds without areas. For example, roadsides and heavily numbers decreased by 99.5 percent, and addressing the grazed rangeland are often sites of nox- seedlings were 20 times more abundant causes of the ious weeds. Weed management needs to 28 on plots that were only mowed once. invasion are focus on how to manage these disturbed Seeding of competitive vegetation areas so they are less open to weeds. As combined with mowing has been particu- doomed because two researchers from the Commonwealth larly successful. Researchers at the Uni- they treat Scientific and Industrial Research Orga- versity of California at Davis showed that symptoms rather nization have written, “attempts to con- seeding of clover, followed by three years trol weeds without addressing the causes of mowing, reduced flower head produc- than causes.” of the invasion are doomed because they tion to zero and reduced fall seedling den- treat symptoms rather than causes. The sities by over 99 percent. It was crucial -- R.J. Hobbs and changes … that allow the initiation or to select a clover variety that competed S.E. Humphries intensification of weed invasion have to strongly with starthistle and was well be addressed before effective weed con- adapted to the site.28 Also, planting of an trol can be achieved.”33 Unless the causes aggressive competitor (vetch) has been of disturbances are identified and elimi- successful without mowing.20 trol.32 Hand-weeding, and hoeing are also nated, noxious weed management is like Burning is useful, especially where fire useful tools. They are most successful running on a treadmill; there is lots of has historically been frequent. At early in the season before the plant has action but little permanent progress. California’s Sugarloaf Ridge State Park, had a chance to develop a large taproot. carefully timed burns have “nearly elimi- Another small-scale management tech- 3. Promote Biological Control nated” starthistle. A single burn reduced nique involves depleting the soil’s seed Most noxious weeds are not native to the number of seeds by 74 percent, and bank with repeated irrigation and culti- the area in which they are a problem. the number of new seedlings by 81 per- vation. Irrigation causes seedlings to ger- Either accidentally or intentionally, they cent. Three years of burns reduced both minate, and then they can be removed have been introduced from around the seed and seedling numbers over 99 per- by disking the area.20 globe. Most noxious weeds have been in- cent. Declines in starthistle were accom- troduced without the insects and diseases panied by increases in the abundance and Lessons Learned that regulate their abundance in their na- diversity of native species.29 What can we learn about management tive range, so they are good candidates Because yellow starthistle is an intro- of noxious weeds in general from look- for biological control. Biological control duced weed, biological control is also a ing at these examples, leafy spurge and is not a silver bullet. It can take years for promising management tool. Potential yellow starthistle? Seven important les- populations of a biological control agent biological control agents include seed sons emerge: to build up enough to impact weed popu- head weevils, seed flies, and seed head lations. Also, biological control needs to gall flies. The one that has the most po- 1. Don’t Panic be done carefully, to avoid irreversibly tential is probably the weevil Eustenopus There’s no need to rush to treat nox- introducing an insect or disease that im-

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pacts native or crop plants.34,35 But, with to mean widespread use of toxic chemi- A three-year summary. Proc. of the 1993 Great Plains Agricultural Council Leafy Spurge Task these caveats, biological control offers “en- cals. Alternative techniques can success- Force Symposium; July 26-28, 1993, Silvercreek, vironmentally safe, energy self-sufficient, fully reduce weed populations and en- CO. Available from U.S. Dept. of Agriculture. ARS. 36 1995. Purge spurge; Leafy Spurge Database. cost-effective, and self-sustaining” man- courage vegetation whose presence is 16. McCoy, P.R. 1997. Angora power. Capital Press agement strategies for noxious weeds. desirable, thus reducing or eliminating the - Idaho edition (June 20):1-2. 17. Dovel, Randy, agronomist, Oregon State Univ. need for repeated treatment. Implement- Klamath Experiment Station. Personal commu- 4. Find Effective Ways to ing nonchemical strategies and reducing nication, February 4, 1998. Reduce Seed Numbers 18. Biesboer, D.D., B. Darveaux, and W.L. Koukkari. the herbicide dependence of noxious weed 1994. Controlling leafy spurge and Canada thistle Weed seeds are future weed popula- programs provides long-term and cost- by competitive species. Final report. Submitted to Minnesota Dept. of Transportation. Office of tions. Reducing the number of seeds in effective weed management. Research Administration. St. Paul, MN, June. the soil, or the number of plant parts 19. DiTomaso, J.M. 1996. Biology of major road- References side weeds. Proc. 48th Annual Calif. Weed Sci. capable of vegetative reproduction, is es- Soc. Pp.69-73. sential. Even though seeds and root buds 1. U.S. Dept. of the Interior. Bureau of Land Man- 20. Thomsen, C. and W.A. Williams. 1992. Yellow agement. Oregon State Office. 1994. Noxious weed starthistle control. Components 3(1):2-6. are often invisible, they hold the key to strategy for Oregon/Washington. Portland, OR, Aug. 21. Coombs, E.M. 1996. Improving biological control long-term successful management. 2. Lorenz, R.J. and R.G. Lym. 1993. A chronology of yellow starthistle with geographic information of leafy spurge research. Proc. Western Weed systems. Proc. of a Symposium on Sustaining Eco- Soc. 46:30-35. systems. Eastern Oregon State College, LaGrande, 5. Encourage Desirable 3. U.S. Dept. of Agriculture. Agricultural Research OR. 29-31 Aug. 1994. Oregon State Univ. Exten- Vegetation Service. Undated. The ecological areawide man- sion Service. Special report No. 953. Pp. 65-70. agement (T.E.A.M.) - Leafy spurge. 22. Gerlach, J.D. Jr. 1997. The introduction, dynam- Sustainable weed management requires www.team.ars.usda.gov. ics of geographic range expansion, and ecosys- 4. Dunn, P.H. 1985. Origins of leafy spurge in North tem effects of yellow star-thistle (Centaurea not just a reduction of weed populations, America. In Watson, A.K. (ed.) Leafy spurge. solstitialis). Proc. 49th Annual Calif. Weed Sci. but also the encouragement of desirable Monograph Series of the Weed Science Society Soc. Pp.136-141. of America. No. 3. Champaign IL. Pp. 7-13. 23. Prather, T.S. 1994. Biology of yellow starthistle. vegetation, the vegetation we’d like to see 5. U. S. Dept. of Agriculture. Animal and Plant Proc. 46th Annual Calif. Weed Sci. Soc. San replace the weed. Unless both issues are Health Inspection Service. 1997. Biological con- Jose, CA. Pp. 219-223. trol of leafy spurge. Program Aid No. 1435. 24. Roché, B. F., C.T. Roché, and R.C. Chapman. addressed, a weed management program 6. Lym, R.G. 1991. Economic impact, classification, 1994. Impacts of grassland habitat on yellow is incomplete and will probably lead to distribution, and ecology of leafy spurge. In James, starthistle (Centaurea solstitialis L.) invasion. L.F. et al. (eds.) Noxious range weeds. Westview Northw. Sci. 68(2):86-91. repeat weed problems. Special Studies in Agriculture Science and Policy. 25. DiTomaso, J.M. 1997. Control of yellow starthistle Boulder CO: Westview Press. Pp. 169-181. with burning, mowing and herbicides. Proc. 49th 6. Experiment With Timing to 7. Marks, J. 1997. This goat likes to pig out. Check Annual Calif. Weed Sci. Soc. Pp.142-145. out these weedeaters. Oregon’s Agricultural 26. E.P. Fuerst. 1996. Physiological characteriza- Improve Success Progress (Fall):15-17. tion of picloram resistance in yellow starthistle. 8. Lesley Richman, U.S. Bureau of Land Manage- Pest. Biochem. Physiol. 56:149-161. The success of many nonchemical ment weed control coordinator, Burns District. 27. Thomsen, C.D., M. Vayssieres, and W.A. Will- management techniques changes dramati- Personal communication, February 4, 1998. iams. Grazing and mowing management of yel- 9. Elliot, T. 1997. Sheep, beetles pair up to control low starthistle. 1994. Proc. 46th Annual Calif. cally depending on the life stage of the leafy spurge. In Hilander, S.K. (ed.) Weeds as Weed Sci. Soc. San Jose, CA. Pp. 228-230. weed at the time the technique is used. teachers: The “many little hammers” weed man- 28. Thomsen, C.D., M. P. Vayssieres, and W.A. Wil- agement alternative. Proceedings of a Novem- liams. 1997. Mowing and subclover plantings For example, mowing of yellow starthistle ber 1995 conference. Helena, MT: Alternative suppress yellow starthistle. Calif. Agricul. (Nov.- increases its abundance if the mowing is Energy Resources Organization. Pp.32-35. Dec.):15-20. 10. McClay, A. 1994. An overview of biological con- 29. Hastings, M.S. and J.M. DiTomaso. 1996. Fire done early in the season, but effectively trol of leafy spurge in Alberta. Abstract of a pre- controls yellow star thistle in California grass- reduces seed and subsequent seedling sentation at the Leafy Spurge Symposium, July lands: Test plots at Sugarloaf Ridge State Park. 1994, Bozeman, MT. Available from U.S. Dept. of Restoration & Management Notes 14(2):124-128. populations if done later in the season. Agriculture. Agricultural Research Service (ARS). 30. Turner, C.E. 1994. Biological control of yellow It’s crucial to determine these effective 1995. Purge spurge; Leafy Spurge Database. starthistle: 1994 update. Proc. 46th Annual Ca- 11. Harris, P. 1991. Classical spurge biological con- lif. Weed Sci. Soc. San Jose, CA. Pp. 224-227. management “windows.” trol with insects and pathogens. U.S. Dept. of 31. Oregon Dept. of Agriculture. Noxious Weed Con- Agriculture. Agricultural Research Service. Proc. trol Program. 1996. Biological control of weeds 7. Use Site-appropriate Leafy Spurge Control Coordination/Planning project summaries: 1996. Salem, OR. Meeting, April 23-25, 1991. Minneapolis, MN. 32. Dremann, C.C. 1996. Grasses and mulch con- Techniques 12. Van Vleet, S. 1994. The establishment, increase, trol yellow-star thistle (California). Restoration & and impact of Aphthona spp. in Fremont County, Management Notes 14(1):79. No one nonchemical technique will Wyoming. (Abstract.) Leafy Spurge Symposium, 33. Hobbs, R.J. and S.E. Humphries. 1995. An inte- be appropriate everywhere. For example, July 1994, Bozeman, MT. Available from U.S. grated approach to the ecology and management Dept. of Agriculture. ARS. 1995. Purge spurge; of plant invasions. Conserv. Biol. 9(4):761-770. sheep grazing is usually unacceptable on Leafy Spurge Database. 34. McEvoy, P.B. 1996. Host specificity and biologi- a nature preserve, but may be appropri- 13. Hansen, R. Undated. Aphthona czwalinae. In cal control. BioScience 46(6):401-404. Weeden, C, T. Shelton, and M. Hoffman (eds.) 35. DeLoach, C.J. 1997. Biological control of weeds ate to manage weeds on a cattle ranch. Biological control: A guide to natural enemies in in the U.S. and Canada. In Luken, J.O., and All techniques should be compatible with North America. Ithaca, NY: Cornell Univ. J.W. Thieret. (eds.) Assessment and manage- www.nysaes.cornell.edu/ent/biocontrol/. ment of plant invasions. New York: Springer- larger management goals. 14. Johnston, A. and R.W. Peake. 1960. Effect of Verlag. selective grazing by sheep on the control of leafy 36. McMurty, J.A. et al. 1995. A historical overview of spurge (Euphorbia esula L.) J. Range Manage. regional research project W-84. In J.R. Nechols, Conclusion 13(4):192-195. et al. (eds.) Biological control in the western United 15. Sedivic, K.K. and R.P. Maine. 1993. Angora goat States. Univ. of California Div. of Agriculture and Noxious weed control does not have grazing as a biological control for leafy spurge; Natural Resources. Publ. 3361. Pp.3-5.

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