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 Managementglyphosate and crushing on firm surfaces extend <strong>the</strong> timeperiod well beyond 10 years. If a more realistic andconservative approach to modeling is used that includesgrowth and seedling inputs, <strong>the</strong>n only <strong>the</strong> use <strong>of</strong> imazapyrapproaches 100% control after four years <strong>of</strong> treatment.Treatment cost per hectare is only a minor component<strong>of</strong> <strong>the</strong> total cost <strong>of</strong> a control effort. Efficacy governs <strong>the</strong>majority <strong>of</strong> <strong>the</strong> total cost. For example, treating 100 hectares<strong>of</strong> Spartina with imazapyr or glyphosate at 38 kg/ha, wouldcost approximately $60,000/ha and $120,000/ha, respectivelyat current chemical prices. These values change dramaticallywhen <strong>the</strong> modeling results shown in Table 1 are factored in.To control 99% <strong>of</strong> Spartina using imazapyr, a total <strong>of</strong> 130 hawould need to be treated over four years at a cost <strong>of</strong>approximately $78,000/ha, whereas to achieve that controlwith glyphosate, a total <strong>of</strong> 208 ha would need to be treatedover seven years at a cost <strong>of</strong> approximately $250,000/ha.DISCUSSIONThe objectives <strong>of</strong> this study were to evaluate <strong>the</strong> Spartinacontrol efforts in Willapa Bay and to determine if <strong>the</strong> efficacy<strong>of</strong> those efforts was sufficient to accomplish eradication.Developing inferences about treatment efficacy based onmonitoring data from a few sites is problematic. Unlikeresearch plots, <strong>the</strong>se treatment sites lack replication andcomplete records on all <strong>the</strong> environmental and site conditions,and in general lack application precision. Traditional “inhouse”monitoring also lacks objectivity. These concerns wereminimized within this study by pooling data collected by animpartial party (WSU) across as many similar treatment sitesand times as possible and using a very conservative estimate<strong>of</strong> control (percent Spartina-free quadrats). The tremendousvariability across sites found in this monitoring effort is notatypical <strong>of</strong> that found in o<strong>the</strong>r Spartina control efforts (Patten2002). Due to <strong>the</strong> lack <strong>of</strong> background data, however, <strong>the</strong>variations in this study are difficult to account for. Detaileddata collection on <strong>the</strong> variables that affect Spartina controlefficacy, such as herbicide dry time, tidal conditions, canopyquality (dirtiness, height, intactness/health, growth stage, andclonal age), spray water quality, and sediment type (Patten2002), are usually not collected by field crews doing <strong>the</strong>control work.Several observations on specific treatments should benoted. Tilling, although a superlative method formechanically controlling Spartina, is costly, requiring anexpensive ($250,000) amphibious tiller and is slow (~0.25ha/hr). It has a limited window during <strong>the</strong> winter when itworks, and unless it is preceded by summer mowing, itresults in massive seedling density <strong>of</strong> more than 200seedlings/m 2 . Crushing is relatively less expensive(~$40,000 to $80,000 for <strong>the</strong> equipment) and is faster (1-2ha/hr) than tilling, but it requires multiple crushing eventsper year. The greatest success in crushing appears to beTable 3. Years to achieve 99% Spartina-free tideland using repeated annualtreatment <strong>of</strong> different control practices.TreatmentExtinctioncoefficient±std. errormean *Calculatedtime toreach 99%Spartinafreetideflat**(years)Amount <strong>of</strong> 100 hameadow Spartinaremaining at <strong>the</strong>start <strong>of</strong> year 5, after 4years <strong>of</strong> treatmentand total amount <strong>of</strong>area treated duringthat time***haremainingtotal hatreatedWinter tilling 0.73±0.03 3.6 1 145Crushing ons<strong>of</strong>tsediment0.52±0.14 6.3 11 211Crushing onsand or firmsilt sedimentGlyphosate9 kg/haGlyphosate38 kg/haCrushing +glyphosate38 kg/haImazapyr 1.7kg/ha0.26±0.09 15.4 73 3600.31±0.06 12.5 52 3230.57±0.04 5.4 7 1920.59±0.04 5.3 6 1850.82 2.7 0.3 127* Extinction coefficient equals <strong>the</strong> mean % Spartina-free quadrats for <strong>the</strong>given treatment.** Assumes that treatment is repeated annually, that <strong>the</strong> equation log0.01/log (1- extinction coefficient) approximates <strong>the</strong> system’s response,and that <strong>the</strong>re are no inputs from spread and seedlings.*** Discrete time, logistic growth model, with growth rate parameter0.15, carrying capacity 100 ha and additional seedling input from outsidesources equal to 0.1% <strong>of</strong> carrying capacity per year. Developed by Dr.Caz Taylor, UC Davis.limited to sites with certain sediment characteristics, such asareas with young Spartina on s<strong>of</strong>t sediment. Crushing wellestablishedSpartina meadows with a thick root mat orSpartina on sand provides marginal control. Disking is alsorelatively inexpensive and comparable to crushing, but wasproblematic in terms <strong>of</strong> sectioning and uprooting large mats<strong>of</strong> Spartina, which re-established in deeper tidal zones. Thebroadcast rate <strong>of</strong> glyphosate, although very inexpensive,only provided control under ideal conditions (>48 hour drytime and a clean, intact canopy). These conditions were rarein <strong>the</strong> field. The hand-sprayed rate <strong>of</strong> glyphosate (with orwithout previous crushing) provided fairly consistentcontrol, but accurate rates and cost analysis are difficult toassess. Tank mixes ranged from 5 to 8% v/v <strong>of</strong> product withspray volumes from 1,000 to 3,000 l/ha spray volume.Application from airboats is limited to a few hectares perday. Variability in efficacy from hand applications largelyreflected plants that were missed or only partially covered.Although large-site monitoring data is lacking, <strong>the</strong> broadcast- 253 -