144 Moore and Lefoe: The Effect of a Heat Wave on Urban Tree Pests in Melbourne usually peaks in December or January in Melbourne, which coincided with Victoria’s periods of extreme heat in 2009. There were four days in January on which temperatures exceeded 40 °C and another eight days over 35 °C before the heat wave in Febru- ary culminating on the 7 February (Figure 1). Lon- gevity of psyllids emerging in Melbourne during this period appears to have been greatly reduced. The optimal time for psyllid control by foliar treat- ment is during the peak adult emergence period, when emerged adult psyllids are vulnerable to contact insecticides. Based on the low number of adults counted on traps, it was considered unnecessary and an unjustifiable expense to implement planned spray- ing during 2008/2009 because without a clearly defined peak, it was not possible to identify the opti- mal timing of treatment, and low adult numbers indi- cated that treatment was unnecessary. CONCLUSION In Victoria, in February 2009 when temperatures rose to 46.4 °C following a heat wave, an unexpected con- sequence of the high temperatures was the killing of many of the mistletoes affecting older eucalypts. Mis- tletoe deaths were also observed in non-eucalypt spe- cies, including Platanus × acerifolia, U. procera, and Pyrus calleryana. The effect of high temperatures, compounded by high winds driving excess water use, in killing mistletoes may have a broader impact on the health and management of urban tree species. Similarly, the reductions in ELB and psyllid infesta- tions of elms and Moreton Bay fig trees after the heat wave and record high temperature day were so great that control measures were not required for several subsequent years. Ongoing monitoring, however, alerted urban tree managers to the rise in ELB num- bers in the summer of 2014 and control measures were implemented in the summer of 2015/2016. Monitoring identifies pest infestation hot spots and allows the appropriate allocation of limited resources. In the areas surveyed, there was no need to under- take mistletoe, psyllid, or ELB control measures for at least five years after the heat wave and high tem- perature day, which impacted upon the work schedules of municipal arborists and tree-related expenditures. There is a strategic opportunity for urban tree managers to integrate climatic events with urban pest control measures. Routine and costly pest control programs could be deferred until surveys indicate that they are ©2020 International Society of Arboriculture needed. While there is a danger that this could lead to complacency where surveys are abandoned, in situa- tions where arboricultural budgets are tight, funds freed from pest control could be allocated to other important arboricultural priorities. Climate change will have a diverse range of effects on the urban forest, making decisions related to plan- ning and management more complex. However, by better understanding tree and pest biology, those responsible for urban forests may be able to use some of the influences wrought by climate change to man- age urban trees and forests more efficiently and proactively. LITERATURE CITED Bennett AB, Gratton C. 2012. Local and landscape scale variables impact parasitoid assemblages across an urbanization gradient. Landscape and Urban Planning. 104:26-33. Boland DJ, Brooker MIH, Chippendale GM, Hall N, Hyland BPM, Johnston RD, Kleinig DA, Turner JD. 1984. Forest trees of Australia. Melbourne (Australia): Nelson-CSIRO. Bowen ME, McAlpine CA, House APN, Smith, GC. 2009. Agricultural landscape modification increases the abundance of an important food source: mistletoes birds and brigalow. Biological Conservation. 142:122-133. Brandt L, Lewis AD, Fahey R, Scott L, Darling L, Swanston C. 2016. A framework for adapting urban forests to climate change. Environmental Science and Policy. 66:393-402. Broadmeadow MSJ, Ray D, Samuel CJA. 2005. Climate change and the future of broadleaved tree species in Britain. Forestry. 78:145-161. Bureau of Meteorology. 2011. Monthly rainfall, Melbourne airport, 1971-2010. Melbourne (Australia): Australian Government. Bureau of Meteorology. 2016. Heatwave service for Australia. Australian Government. [Accessed 24 June 2016]. http:// www.bom.gov.au/australia/heatwave Calder DM, Bernhardt P. 1983. The biology of mistletoes. Sydney (Australia): Academic Press. Clair DJ. 1986. Bionomics of the elm leaf beetle, Xanthogaleruca luteola (Muller), in north eastern California [PhD thesis]. Berkeley (CA, USA): University of California. Clark JS, Bell DM, Hersh MH, Nichols L. 2011. Climate change vulnerability of forest biodiversity: climate and competition tracking of demographic rates. Global Change Biology. 17:1834-1849. Commissioner for Environmental Sustainability. 2012. Foundation paper one: climate change Victoria. The State of Victoria: Commissioner for Environmental Sustainability. Dahlsten DL, Tait SM, Rowney DL, Gingg BJ. 1993. A moni- toring system and developing ecologically sound treatments for elm leaf beetle. Journal of Arboriculture. 19:181-186. Danby RK, Hik DS. 2007. Variability, contingency and rapid change in recent subarctic alpine treeline dynamics. Journal of Ecology. 95:352-363.
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