Arboriculture & Urban Forestry 44(3): May 2018 cial Fraxinus × ‘Northern Treasure’ ash, which is a black ash (F. nigra) × Manchurian ash hybrid (Herms 2015; Rebek et al. 2008), further under- scores the need for continued research attention in this area. In 2004, right when EAB started to impact Toledo, Ohio, U.S., an urban plantation was established there by The Ohio State Univer- sity Extension; the site was approximately 53 km south of the original EAB infestation (Detroit, Michigan, U.S.). The plantation was established to evaluate the interspecific variation in ash tree mortality due to EAB in several cultivars and seedlings of ash. The trees were monitored for growth and mortality due to EAB on an annual basis. In this short communication, researchers present the results and discuss the research im- plications stemming from the monitoring effort. METHODS The plantation included a total of 156 ash trees, composed of 9 ash species (17 ash cultivars and 2 ash seedlings). Two 30 m wide median strips, approximately 50 m apart from each other, were chosen to plant the trees with a plant spacing of 7.62 m. The plantings were installed using a com- pletely randomized design during April–May in 2004 and 2005, depending on the availability of the planting material. A list of trees planted, their number, and their source is provided in Table 1. Cultivars (named and unnamed; see Table 1) were generally planted as 1.2–1.5 m whips, while seed- lings were generally less than 30 cm tall at plant- ing. The trees were never treated with pesticides to control EAB and were never irrigated. Plants were mulched with uncomposted hardwood chips. The trees were evaluated annually (once between June and September) for tree growth [diameter breast height (DBH) measured at 1.3 m off the ground; for trees shorter than 1.3 m, the DBH was noted as zero]. The trees were visually inspected for any apparent symptoms of EAB infestation, including D-shaped exit holes, bark splitting, and serpen- tine galleries. Each year, the trees were classified as healthy, possibly infested, or dead. A tree was con- sidered dead because of EAB when all the branches or crown above 1.3 m were dead along with the presence of EAB symptoms. Data reported in this paper include years between 2004 and 2016. The data for 2007 was lost during the transition when 155 a student who collected the data graduated from the university. Henceforth, data from 2007 are not presented in the results. Although data on visual symptoms of EAB infestation were collected annu- ally, only data on mortality (i.e., dead versus alive) is presented in this study, as researchers did not conduct an exhaustive survey of EAB infestation. RESULTS At the end of the 12-year monitoring period in 2016, the DBH of trees across all ash species ranged between 17 cm and 31 cm, with an average DBH of 24.2 cm. The trees that were planted as true seed- lings, including black ash and Manchurian ash, had the smallest average DBH (18.9 cm and 17 cm respectively). The two narrowleaf ash cultivars of European origin (F. angustifolia subsp. angustifo- lia cv. ‘Desert’ and F. angustifolia subsp. oxycarpa cv. ‘Raywood’) showed the greatest average diam- eter growth (30.6 cm and 31 cm, respectively) de- spite their smaller size at planting (Figure 1). The ‘Northern Treasure’ ash had an average DBH of 28.7 cm aſter 12 years. Even though the trees that were planted as seedlings were small at the time of planting, most of the trees had grown to an EAB infestable size of 2.5 cm (Herms and McCullough 2014) by 2008. The trees that were smaller than 2.5 cm in 2008 included one black ash seedling, one blue ash (F. quadrangulata) seedling, two green ash seedlings, and three Manchurian ash seedlings. All trees had grown to an infestable size by 2010. Aſter discounting the 20 trees (13% of the 156 total trees) that were lost due to reasons other than EAB [failure to establish (n = 15), deer and mechan- ical damage (n = 5)], the overall survival rate in 2016 was 45% (62 trees) (Table 1). In all, 55% of the 136 trees were declared dead from EAB aſter 12 years. Of the surviving trees, only Manchurian ash and blue ash had all of the planted trees surviving in 2016 (aſter discounting the three Manchurian ash and two blue ash trees that were lost to reasons other than EAB). Followed by the aforementioned ashes, the ‘Northern Treasure’ ash, as well as the two white ash (F. americana) cultivars ‘Rosehill’ and ‘Autumn Purple’, exhibited higher survival rates (83%, 78%, and 71%, respectively; Table 1). Among the black ash cultivars, the ‘unnamed culti- var’ exhibited higher survival rate (57%) than ‘Fall Gold’ (0%). Similarly, ash cultivars of European ©2018 International Society of Arboriculture
May 2018
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