Proceedings of the Third International Conference on Invasive ...

Chapter 4: Spartina Control and Management<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive Spartinaapplication <strong>of</strong> imazapyr conducted in 2004 was relativelyinexpensive (~$600/ha), fast (>100 ha/day), and fairlyefficacious.Repeated control measures conducted year after year on<strong>the</strong> same site should result in an overall reduction <strong>of</strong>Spartina at <strong>the</strong> site. This overall reduction in Spartinaoccupation over time (two years) was not evident from <strong>the</strong>pooled monitoring data for ei<strong>the</strong>r chemical or mechanicalcontrol. These results are not inconsistent with those foundin Puget Sound (Hacker et al. 2001). They report that sitesrequired consistent control for four years to obtain an 86%decrease in Spartina. Most <strong>of</strong> <strong>the</strong> sites monitored in thisstudy were also large (>10 ha) and, according to Hacker etal. (2001), less likely to show decline in Spartina densityover time than small sites. Examples <strong>of</strong> this spatial scaleeffect were evident in this study. For three discrete sites thatwere smaller than five hectares and sprayed for twoconsecutive years, <strong>the</strong> percentage <strong>of</strong> Spartina-free quadratswent from 73% to 85%, 60% to 90% and 60% to 95%.Evidently on large sites, re-growth and seedling reinfestationcompensated for any additional control achievedin subsequent years. This concurs with results from <strong>the</strong>discrete time, logistic growth model. When parameters forgrowth rate are set at 0.15, seedling input at 0.01, andcontrol rates at 50%, 10 ha <strong>of</strong> Spartina within a 100-hamudflat would still have 50% <strong>of</strong> Spartina left in <strong>the</strong>beginning <strong>of</strong> <strong>the</strong> third year. On <strong>the</strong> o<strong>the</strong>r hand, when acontrol rate <strong>of</strong> 73% is used and <strong>the</strong> parameter for outsideseedling input is reduced to 0.005, <strong>the</strong> site is projected to be81% Spartina-free in <strong>the</strong> beginning <strong>of</strong> <strong>the</strong> third year (this issimilar to <strong>the</strong> 85% found at one <strong>of</strong> our monitoring sites).Three major conclusions can be reached from thismonitoring study. First, real world control data are highlyvariable between sites and years, and tend to show resultsthat are less effective than what would be expected underideal conditions. Efficacy can vary by at least 20% from <strong>the</strong>expected level. Second, with <strong>the</strong> exceptions <strong>of</strong> tilling andimazapyr, none <strong>of</strong> <strong>the</strong> treatments provided efficacyanywhere near <strong>the</strong> level <strong>of</strong> that which would be required toachieve eradication in a reasonable time frame. Based on <strong>the</strong>political landscape, it is not prudent to expect funding for alarge-scale control effort to go beyond a six to eight-yeartime period. Thus, unless <strong>the</strong> average control rate for a givenmethod can be expected to be greater than 75%, that methodhas minimal practical value. The tenfold expansion <strong>of</strong>Spartina in Willapa Bay during <strong>the</strong> last decade <strong>of</strong> controlefforts testifies to this maxim. <strong>Third</strong>, even if <strong>the</strong> control rateis 75%, as long as <strong>the</strong>re is significant seedling input fromoutside sources, eradication can not be achieved. The controlefforts should be mounted over a scale large enough tominimize threats from new seedlings. Similarly, unless <strong>the</strong>sites continue to be treated year after year, no appreciablegains toward eradication can be achieved.ACKNOWLEDGEMENT:Funding was provided by Willapa National WildlifeRefuge and Washington State Commission for PesticideRegistration. The discrete time, logistic growth model wasdeveloped and provided by Dr. Caz Taylor, UC Davis.REFERENCESFrid, C., W. Chandrasekara, and P. Davey, 1999. The restoration <strong>of</strong>mud flats invaded by common cordgrass (Spartina anglica)using mechanical disturbance and its effects on <strong>the</strong> macrobenthicfauna. Aquatic Conservation: Marine and FreshwaterEcosystems 9:47-61.Garnett, R.P., G. Hirons, C. Evans, and D. O’Connor. 1992. Thecontrol <strong>of</strong> Spartina (cord-grass) using glyphosate. Aspects <strong>of</strong>Applied Biology 29:359-364.Government Accounting Office. 2002. Invasive Species: Clearerfocus and greater commitment needed to effectively manage <strong>the</strong>problem. GAO-03-1; www.gao.gov/cgi-bin/getrpt?GAO-03-01.Hacker, S.D., D. Heimer, S. E. Hellquist, T.G. Reeder, B. Reeves,T.J. Riordon, and M.N. Dethier, 2001. A marine plant (Spartinaanglica) invades widely varying habitats: potential mechanisms<strong>of</strong> invasion and control. Biological Invasions 3: 211-217.Hedge P., L. Kriwoken and K. Patten, 2003. A review <strong>of</strong> Spartinamanagement in Washington State, US. Journal <strong>of</strong> Aquatic PlantManagement 41: 82-90.Kilbride, K.M., F.L. Paveglio and C.E. Grue, 1995. Control <strong>of</strong>smooth cordgrass with Rodeo in a southwestern Washingtonestuary. Wildlife Society Bulletin 23:53-524.Major, W.W., III, C.E. Grue, J.M. Grassley and L.L. Conquest,2003. Mechanical and chemical control <strong>of</strong> smooth cordgrass inWillapa Bay, Washington. Journal <strong>of</strong> Aquatic PlantManagement 41: 6-12.Patten, K. 2002. Smooth cordgrass control with imazapyr. WeedTechnology 16: 826-832.Patten, K. 2003. The efficacy <strong>of</strong> mechanical treatment efforts in2001 on <strong>the</strong> control <strong>of</strong> Spartina in Willapa Bay in 2002. Progressreport submitted to <strong>the</strong> Willapa National Wildlife Refuge.(Available from <strong>the</strong> author via email [pattenk@wsu.edu].)Patten, K. 2004. 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Department <strong>of</strong> Conservation and NaturalResources, Yarram, Victoria, pp. 66.Shaw, W. B. and D.S. Gosling. 1995. Spartina control in NewZealand—an overview. In: J.E. Rash, R.C. Williamson, and S.J.Taylor, eds. <strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> Australasian <strong>Conference</strong> onSpartina Control Melbourne, Australia: Victorian GovernmentPublication. pp. 43-60.WSDA. 1999-2003, Spartina Eradication Program—LegislativeReports, http://agr.wa.gov/PlantsInsects/Weeds/Spartina.- 254 -