132 researchers to detect EAB early in the invasion, before trees began to decline in health in Lafay- ette. This early detection is likely attributable to annual surveys, underscoring the importance of examining threatened street trees in regions where EAB infestations have been reported. The use of visual surveys by trained arborists and ur- ban foresters could drastically reduce the time between EAB colonization and their detection in an urban forest. One hundred fifty-nine ash trees were surveyed, only a subset of the 1,500 ash street trees in the greater Lafayette area, which drastically reduced time spent in the field. More- over, such visual surveys are also faster and less costly than using girdled trap trees where the bark must be carefully removed to count larvae at the end of the season (Cappaert et al. 2005). Analysis of ash decline during the course of this study is consistent with the wave analogy. The vigor of ash trees declined faster in Indianapolis than in Lafayette (Figure 1). However, trees in Lafayette began to decline more rapidly the year aſter EAB was detected (Figure 2). Moreover, in the third year, EAB was more likely to be detected in Lafay- ette in trees of poor quality. Interestingly, at the end of the study, trees in Lafayette displayed an average vigor ranking similar to trees in Indianapolis two years prior, suggesting that Lafayette is entering the crest phase of the invasion. The decline among sentinel trees in the more recently infested Lafay- ette area may serve as a warning that EAB popula- tion levels are growing, and action must be taken to save ash trees and to protect the urban forest. A limitation of the visual assessment scheme is that it does not account for EAB infesting higher portions of the main stem and branches of the canopy. For taller trees, inspecting the basal two meters of the bole will not account for emergence holes higher in the tree, and using binoculars to survey the canopy might yield earlier detection of EAB (Smitley et al. 2008). Nevertheless, the majority of street trees in Midwestern U.S. cities are small or young (Peper et al. 2008; Nowak et al. 2013), and street trees in urban settings oſten grow slower than those in natural forests (Iakovoglou et al. 2001). In fact, only a few street trees in the cur- rent study had a bole greater than two meters. In these smaller trees, EAB may attack the bole earlier, making surveys of this portion of the trunk more ©2015 International Society of Arboriculture Hughes et al.: Borer-Specific Assessment Scheme informative for early detection efforts. Using the visual assessment scheme in Lafayette, for exam- ple, researchers were able to detect EAB emergence holes on the lower bole of apparently healthy trees, suggesting that the method of rapid assessment is capable of detecting an emerging EAB invasion even before trees begin to show signs of decline. In this study, tree vigor influenced the coloni- zation behavior of EAB, supporting hypotheses that it can be a putative predictor of EAB attack in areas with an active infestation (McCullough et al. 2009a; McCullough et al. 2009b). Stress predis- poses Asian ash trees to attack by EAB in its native range (Yu 1992), and EAB are more attracted to girdled and herbicide-treated ash trees than healthy trees (Poland et al. 2005; Marshall et al. 2009; McCullough et al. 2009a; McCullough et al. 2009b). Moreover, EAB oſten attacks trees that have already been colonized, as demonstrated by data from the Indianapolis sites. Larvae may even improve the suitability of a tree for further infestation as they feed, stressing the tree and making it more attractive through changes in its volatile profiles (Rodriguez-Saona et al. 2006) or by increasing the nutritional quality of the host. Likewise, native Agrilus beetles in North America also attack stressed trees. Oaks (Quer- cus spp.) and birches (Betula spp.) are susceptible to A. bilineatus and A. anxius, respectively, when stressed by drought and other factors (Ander- son 1944; Haack and Benjamin 1982; Dunn et al. 1986; Dunn et al. 1987; Katovich et al. 2001). Of the general predictors of EAB, canopy thin- ning was positively correlated with EAB emergence holes (Figure 5). Epicormic sprouts, woodpecker damage, and bark splits had little relationship with EAB emergence holes and may be less useful for early detection efforts. Canopy thinning is closely associated with the vigor ranking system, but it may be a valuable predictor on its own. However, canopy thinning is a symptom of many biotic and abiotic stresses, including drought. Thus, care should be taken when using canopy thin- ning to detect emerald ash borer in urban trees. Researchers also found that apparently healthy trees are susceptible to EAB. Using the borer- specific assessment scheme, the first incidence of EAB was identified in Lafayette, Indiana. In 2011, one tree rated as Fair was found to have EAB, and
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