Willow Sawfly Management Trials - Weeds Australia

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Willow Sawfly Management Trials - Weeds Australia

262.3 Results2.3.1 Willow Sawfly Population LevelsWillow sawfly populations were maintained at low levels in the 2009/10 season at most siteswhere they had been low in the 2008/09 season – Beechworth, Healesville, Leneva West andTarago (Table 8) and consequently no tree defoliation was observed at these sites (Table 9).High willow sawfly populations continued to persist at the Everton and Kergunyah sites (Table8), as had been the case in previous seasons. The highest numbers of larvae were found atEverton in December on the black, crack and golden willows, while at Kergunyah populationlevels were highest in March (Table 8). There was some oscillation of larvae numbers throughthe season as site visits coincided with different stages of the population development cycle.Table 8: Willow Sawfly Populations Assessed Throughout the 2009/10 Season on VariousWillow Taxa at Monitoring SitesSiteWillowTaxaAverage Number of Willow Sawfly Larvae Found in 5Minute CountOct/Nov09Dec 09 Jan 10 Mar 10 Apr 10Baranduda Black - 1 22 1 - 25Beechworth Grey - 1 2 - 0Everton Black 2 108 23 1 4Crack 3 167 2 40 9Golden 0 111 14 16 2Purple 0 56 0 0 0Weeping 0 22 - 0 0Happy Valley Crack 2 16 76 22 13Healesville Crack 0 4 1 1 1Kergunyah S. x rubens 4 18 7 72 11Kiewa Crack 2 8 0 1 1Weeping 0 6 0 0 0Leneva Crack - 7 1 - 5Pussy - 0 0 - 0Weeping - 1 0 - 0Tarago S. x rubens 0 2 2 10 61 Some sites were not assessed at every monitoring point throughout the seasonAt the remaining sites, willow sawfly populations in the 2009/10 season developed differently incomparison with previous seasons. Willow sawfly populations had been high at the Kiewa sitesince willow sawfly was reported in north-east Victoria in December 2005. However,populations failed to increase to high levels in 2009/10 on either the crack or weeping willows(Table 8). As a consequence, no tree defoliation was noted at this site (Table 9). It is unclear whywillow sawfly numbers were so low at Kiewa this season.

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