Arboriculture & Urban Forestry 36(4): July 2010 MDA established a 0.8 km buffer zone around the nursery and all ash trees within this zone were removed and destroyed by March 2004. From 2004 to 2006, MDA established and monitored 300 trap trees and initiated surveys to locate ashes in the quarantine area. In May 2004, EAB was detected at two landscape sites, but rapid destruction of the trees and intensive re-inspection of re- maining trees revealed no further signs of activity. An aggressive public education campaign and subsequent follow-up by MDA staff on hundreds of homeowner calls and site visits throughout central Maryland resulted in no additional detections of EAB. The absence of further detections of EAB in 2004 and lack of detec- tions in 2005 fueled hopes that EAB was eradicated in Maryland. In August 2006, EAB was detected in a trap tree planted near the nursery and on a girdled native tree outside the eradication zone where trees were removed, but still within the federal quar- antine zone. These events initiated an intense, expanded survey that resulted in additional new detections. It was assumed the new detections dated from the initial infestation in 2003 and the eradication zone was expanded 2.4 km at that time to account for potential movement of the pest over the previous three years. Between 2006 and 2008 thousands of new EAB detections were made, as evidenced by exit holes and active galleries in debarked trees, and by 2008 more than 40,000 ash trees had been removed on more than 73 km2 in Prince George’s County. On August 18, 2008, EAB were detected in Charles County, more than 7.24 km south of the original infestation site in Prince George’s County. The objective of this research was to determine the rate of spread of EAB in a quarantine zone where aggressive intervention tactics, including destruction of infested and uninfested hosts, extensive surveillance, and public education limited the dispersal of this pest. Our overarching goal is to help arborists and urban foresters under- stand the rate of spread of EAB and provide empirical information to help them develop plans to deal with the management of this pest. MATERIALS AND METHODS Under the guidance of the National EAB Science Panel, a meth- odology for survey and recordkeeping was established for quar- antine and eradication programs in Maryland. The 2003 infesta- tion at the nursery in southern Prince George’s County served as the center of the EAB infestation in Maryland. Using Geographic Information System (GIS), a map was generated for a project area 8.05 km square subdivided into 0.01 km² plots with the nurs- ery at the center. Distances for all EAB detections were made from a point in the Maryland nursery centrally located between the two blocks of Michigan ash trees to the center of the 0.01 km² grid cell within which the initial infestation was detected. Thousands of EAB were detected from 2006–2008. Some- times clusters of trees with EAB larvae or exit holes were con- centrated in an area and sometimes detections occurred in a single, isolated tree. Each year four distinct sample grid cells were selected at the leading edge of the beetle’s distribution to be included in the analysis. Each sample grid cell, hereafter called foci, represented a distinct tree or group of trees separated from other foci by several grid cells surveyed during the same year that yielded no EAB detections through debarking both senti- nel trees and 10% of native trees within a 0.8 km buffer zone outside the eradication zone, and the absence of adult beetles on purple sticky traps. Foci selected for analysis in each year were those most distant from the epicenter irrespective of direction. 161 Examination of the detection points in 2006 revealed four dis- tinct foci (Figure 1). One focus consisted of a single street tree NNW of the epicenter. A second focus was a single native tree lo- cated northwest of the epicenter. The third focus was a single na- tive ash northeast of the epicenter and the last focus consisted of hundreds of native and managed ashes southeast of the epicenter. In 2007, three new foci were detected and one existing focus in- cluded in 2006 expanded outward to adjacent grid cells. A focus of several native trees was detected north of the epicenter (Figure 1). A single native tree was detected southwest of the epicenter. Approximately 20 infested native trees were detected west of the epicenter, and the large focus detected southeast of the epicenter in 2006 expanded farther southeast in 2007. In 2008, four new foci were detected (Figure 1). Nearly five miles south of the epi- center, dozens of infested native trees were detected. This detec- tion expanded the eradication zone from Prince George’s County to include Charles County, MD. Southeast of the epicenter, a sin- gle native tree was detected and southwest of the epicenter two native trees were detected. In late December 2008, a single street tree northwest of the epicenter was confirmed to be infested. To determine the average rate of advancement of the lead- ing edge, the study authors regressed the distances of the 12 foci (four foci for each of three years) from the nursery against time (years), from the first detection in 2003. The slope of the rela- tionship between distance and time represents the average rate of spread of emerald ash borer in kilometers per year. To estimate a maximum rate of spread for EAB, the distance of the furthest Figure 1. Map of Maryland EAB Project detections from 2003 to 2008, showing epicenter at nursery surrounded by initial 2003 eradication zone, and the four most distant emerald ash borer detections each year in 2006, 2007, and 2008. ©2010 International Society of Arboriculture
July 2010
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