©2023 International Society of Arboriculture & URBAN FORESTRY Volume 49, No. 1, January 2023 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) CONTENTS Erratum .......................................................................................................................................... 1 C.W. Johnson, R.O. Olatinwo, J. Hwang, and C. Brownie Effi cacy of Propiconazole for Prevention of Sassafras Mortality from Laurel Wilt Disease Using a Tree Micro-Injection and Micro-Infusion Delivery System .............................. 2 Abstract. Laurel wilt is a lethal disease of American Lauraceae caused by Harringtonia lauricola. Propiconazole is a systemic fungicide which arrests fungal growth among a variety of plant hosts. Propiconazole as a preventive treatment against laurel wilt in sassafras (Sassafras albidum) has not been evaluated. We treated sassafras trees with propiconazole using the Arborjet QUIK-jet® Micro-InjectionTM and TREE I.V. Micro- InfusionTM systems (Arborjet,Inc., Woburn, MA, USA) and challenged trees by inoculating them with H. lauricola. Out of 7 trees treated using the QUIK-jet Micro-Injection system, 6 (86%) survived 52 or more weeks following inoculation with H. lauricola, while only 11% of inocu- lated control trees (1 of 9) survived over this period. All trees not damaged by hurricanes (n = 13) treated with propiconazole using the TREE I.V. Micro-Infusion system survived signifi cantly longer than untreated control trees after inoculation with H. lauricola; 10 of 13 trees (77%) survived with < 50% crown loss, and 8 of 13 trees (62%) appeared entirely healthy 54 weeks post-inoculation. In the TREE I.V. Micro-Infusion system trial, 15 of 19 control trees (79%) had either died or lost ≥ 50% of living crown 54 weeks post-inoculation with H. lauricola. Results indicate sassafras trees treated with propiconazole using the Arborjet QUIK-jet Micro-Injection and TREE I.V. Micro-Infusion systems are sig- nifi cantly less likely to die within one year of infection with H. lauricola; however some trees may exhibit signifi cant crown decline (≥ 50%) over this period. Keywords. Ambrosia Beetle; Bioassay; Fungicide Infusion; Fungicide Injection; Harringtonia lauricola; Propiconazole; Raffaelea lauricola; Redbay; Sassafras albidum; Xyleborus glabratus. G.M. Moore and A. Chandler The Potential of Yellow Gum (Eucalyptus leucoxylon F. Muell.) as an Urban Street Tree: An Assessment of Species Performance in the City of Greater Melbourne, Australia .......... 16 Abstract. Background: In contrast to trees from northern hemisphere genera, there has been little research into the selection and vegetative propagation of Australian native tree species for use as street trees. Eucalyptus leucoxylon F. Muell. is one of a few eucalypts occurring in south-eastern Australia with bright coloured fl owers and is highly regarded as an ornamental tree that fl owers readily. It is propagated from seed, but progeny typically show seedling variability and diversity. Eucalyptus leucoxylon was identifi ed as the most widely planted eucalypt in the streets of the city of greater Melbourne, Australia. Methods: This research assessed 300 E. leucoxylon street trees growing across the city of greater Melbourne for their performance against arboricultural criteria relating to canopy structure and density, straightness of the trunk, health (assessed on canopy, trunk, and branch condition, production of exudates, and presence of fungal fruiting bodies), fl ower colour, and root systems. Results: The results showed that E. leucoxylon was a suitable street tree species with most specimens showing good habit, vigour, and health. Discussion: The trees had traits such as live crown ratio, height, fl ower colour, and capacity to cope with pruning that are considered appropriate for a street tree. Their dense canopies and high live crown ratios provide shade that can reduce the urban heat island (UHI) effect. Conclusion: This suggests the species has the potential to be a successful street tree not only in Australia, but in other parts of the world where it has been grown successfully in forestry plantations. Keywords. Arboricultural Criteria; Eucalyptus; Flower Colour; Live Crown Ratio; Street Tree Performance; Urban Forest. ARBORICULTURE
January 2023
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