138 Moore and Lefoe: The Effect of a Heat Wave on Urban Tree Pests in Melbourne of dead ELBs were discovered below the canopies of street tree elms after 4 pm on 7 February, data were sought on the levels of ELB damage to leaves, which are indicative of ELB numbers, recorded in surveys before and after the heat event and on the subsequent level of ELB control measures undertaken in the years after the heat wave and record hot day. Data were available from the Department of Environment and Primary Industry (DEPI) and the Urban Forest Group of the Melbourne City Council for ten targeted loca- tions: Epsom and Flemington Roads, Powlett, George and Clowes Streets, Fitzroy and Carlton Gardens, Alexandra Avenue, Royal Parade, and Fawkner Park. At each location, ELB damage was determined using a point rating scale of the percentage of leaf damage where damage up to 10% of the leaf area removed was rated as 1, up to 20% as 2, up to 30% as 3, up to 100%, which was scored as 10. The sites were surveyed fortnightly in December 2008, and then from January until March 2009, and again from November to March in 2009/2010, 2010/2011, 2012/2013, and 2013/2014. The best estimate of the full extent of ELB grazing on tree species is made when the leaves of trees are assessed for damage after the ELBs have completed their grazing late in the growing season. For this reason, only data for late-season grazing levels are presented in this paper, as these best represent seasonal damage to trees and reflect beetle numbers that allow annual comparisons to be made. Control measures for ELBs were under- taken when a rating of 1 or more was recorded for high-profile sites and when scores exceeded 2 for less prominent sites. Figs and Psyllids Psyllid egg-laying in Melbourne usually occurs from late-October to early-February, with adult emergence ceasing in mid-autumn (early April)(Honan and McArthur 1998). The City of Melbourne with Agri- culture Victoria Services Pty. Ltd had monitored fig psyllid infestation using protocols and sample sizes recommended by Honan and McArthur (1998). Leaf samples were examined from figs growing at 12 sites across Melbourne from 19 November 2008 through 6 March 2009. Trees within each site were selected ran- domly and, for each sample, branch terminals (approximately 40 cm long) were examined from the ground or by cutting with pole pruners. They were examined from varying heights (to 4 m) and distances from the trunk, and from each direction (north, south, ©2020 International Society of Arboriculture east, and west) around the tree until 50 leaves were available for examination. The number of lerps with living nymphs beneath them on each leaf was recorded and then doubled to obtain an average num- ber of living psyllids per 100 leaves (Honan and McArthur 1998). Control measures were recom- mended when an infestation level above 25 psyl- lids/100 leaves was recorded. Similar sampling was done in 2005 and data are presented for comparison with 2008 and 2009. Yellow sticky traps were placed in trees in Princes and Fawkner Parks to trap flying adult psyllids. Traps were checked and replaced weekly from 19 November 2008 through 6 March 2009, when they were discontinued, as no living psyl- lids were recorded for three successive sampling peri- ods. The psyllid monitoring was funded to inform the Melbourne City Council’s pest management pro- gram, but there was so little psyllid activity that sur- veys were not funded from 2010 through 2013. The data comparing mistletoe, ELB, and psyllid infestation levels before and after 7 February 2009 did not conform to the assumption of a normal distri- bution and so the Mann-Whitney test was applied (White and White 1996). RESULTS River Red Gum and Mistletoes The survey data on mistletoe occurrence on river red gum, E. camaldulensis, show that mistletoe numbers were significantly reduced after the extreme weather and subsequent occurrence rates have remained low (Table 1). Living mistletoe numbers were signifi- cantly lower 1 month and 30 months after the hot day when compared to the numbers prior to 7 February (P < 0.01 for both comparisons). None of the 46 sur- veyed eucalypts died during or after the hot day, and in the two years that followed, above average rainfall resulted in the trees refoliating and having higher density canopies. Of the 237 mistletoes present on the E. camaldulensis before 7 February 2009, 210 (88.6%) were killed. The data also reveal that mistletoe numbers have continued to remain low for a period of five years (P < 0.01) after 7 February (Table 1) and that there was a low incidence of new mistletoe establishment, with only nine new mistletoes establishing on the trees over that period. No new mistletoes established on the young or semi-mature trees surveyed, but mature trees were susceptible to infestation (Figure 2).
March 2020
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