Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 4: Spartina Control and ManagementBIOLOGICAL CONTROL OF SPARTINAF. S. GREVSTAD 1 ,M.S.WECKER 1 , AND D. R. STRONG 21 Olympic Natural Resources Center, University <strong>of</strong> Washington, P.O. Box 1628, Forks, WA 98331;grevstad@u.washington.edu2 Department <strong>of</strong> Evolotion and Ecology, University <strong>of</strong> California, Davis, CA 95616Biological control using introduced natural enemies can be an effective approach to <strong>the</strong> long termcontrol <strong>of</strong> widespread weeds. A biological control program against Spartina spp. is underway inWashington State, where more than 10,000 hectares (ha) <strong>of</strong> intertidal mudflat are affected bySpartina alterniflora and Spartina anglica. Releases <strong>of</strong> <strong>the</strong> planthopper Prokelisia marginata havebeen made into Willapa Bay each year since 2000 and into Puget Sound since 2003. Prior tointroducing this insect, rigorous host specificity testing and a review by <strong>the</strong> Technical AdvisoryGroup on Biological Control <strong>of</strong> Weeds confirmed that <strong>the</strong> risk to non-target plants was minute.Populations <strong>of</strong> <strong>the</strong> biocontrol agent were initially slow to establish and grow. However, earlyproblems with high winter mortality have been remedied through a combination <strong>of</strong> improved releasesite selection and <strong>the</strong> use <strong>of</strong> cold-hardy east coast biotypes. At least two populations in Willapa Bayare well established and expanding. At a localized scale, we have measured 50 percent reductions <strong>of</strong>Spartina biomass and 90 percent reduction in viable seed set due to P. marginata. The full extent <strong>of</strong><strong>the</strong> impact will only be known with time.While <strong>the</strong> use <strong>of</strong> biological control in California may pose a risk to <strong>the</strong> closely related nativeSpartina foliosa, it would be an excellent option in o<strong>the</strong>r o<strong>the</strong>r parts <strong>of</strong> <strong>the</strong> world where Spartina hasinvaded and where <strong>the</strong>re are no closely related native Spartina species. In addition to P. marginata,o<strong>the</strong>r candidate biocontrol agents from <strong>the</strong> Atlantic Coast are currently being investigated.Keywords: Biological control, Spartina alterniflora, Spartina anglica, Prokelisia marginata,Willapa Bay, Puget SoundINTRODUCTIONClassical biological control <strong>of</strong> a pest or weed involves<strong>the</strong> introduction <strong>of</strong> a natural enemy (biocontrol agent) fromano<strong>the</strong>r geographic region. The goal is to establish apermanent population <strong>of</strong> <strong>the</strong> biocontrol agent that willprovide long-term control. During <strong>the</strong> last century, close to1,000 biological control introductions for weeds were madethroughout <strong>the</strong> world (Julien and Griffiths 1998). Modernweed biocontrol projects in <strong>the</strong> United States proceed onlyafter extensive testing <strong>of</strong> <strong>the</strong> natural enemy followed by areview by <strong>the</strong> federal Technical Advisory Group onBiological Control <strong>of</strong> Weeds to ensure that it will not harmo<strong>the</strong>r organisms. Weed biocontrol has proven to be a safeand <strong>of</strong>ten very effective method <strong>of</strong> long term control <strong>of</strong>widespread invasive plants (Cruttwell-McFadyen 1998).Biological control has both advantages anddisadvantages over traditional control. Unlike most chemicaland mechanical approaches, biological control is highlyspecific to <strong>the</strong> target weed. Since biological control agentshave been chosen for <strong>the</strong>ir host specificity, <strong>the</strong>y will notharm o<strong>the</strong>r plant species intermixed with <strong>the</strong> weed.Biological control is economical over large areas. Onceestablished, <strong>the</strong> biological control agent will reproduce,spread to new sites, and continue to damage <strong>the</strong> plant withlittle or no additional input. Biological controls have notoxic residues or health hazards as do some herbicides.When it is successful, biological control can provide apermanent solution to a weed problem, although it usuallymaintains a very low level <strong>of</strong> infestation ra<strong>the</strong>r than bringingabout full eradication.The disadvantages <strong>of</strong> biological control include <strong>the</strong>large amount <strong>of</strong> pre-release research that is required.Moreover, even with careful selection <strong>of</strong> host-specificagents, <strong>the</strong>re will always be some small risk to non-targetorganisms from ei<strong>the</strong>r direct or indirect interactions.Biological control is <strong>of</strong>ten slow in its action, taking severalyears and even up to a decade for an impact to be seen.Finally, <strong>the</strong> complexities <strong>of</strong> ecological interactions mean that<strong>the</strong> effectiveness <strong>of</strong> biological control is difficult to predictahead <strong>of</strong> time. The probability <strong>of</strong> successful controlincreases when multiple biocontrol agents are used (Deno<strong>the</strong>t al. 2003).A biological control program for Spartina alternifloraand Spartina anglica in Washington State was developedduring <strong>the</strong> late 1990s. The biocontrol agent Prokelisiamarginata, a sapsucking planthopper, was introducedbeginning in 2000. In this paper, we provide backgroundinformation about this biological control program. Then wepresent results <strong>of</strong> a comparison <strong>of</strong> <strong>the</strong> performance <strong>of</strong> four- 267 -