Willow Sawfly Management Trials - Weeds Australia

More documents

Recommendations

Info

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.
High willow sawfly numbers were also found at the Baranduda site in both 2007/08 and 2008/09,although tree defoliation only occurred in 2007/08 (Ede et al. 2009). In the 2009/10 season,willow sawfly numbers were low throughout the season (Table 8) and no tree defoliation wasobserved (Table 9).In contrast, after three seasons of very low populations, willow sawfly numbers at Happy Valleyincreased to high levels (Table 8), and caused considerable tree defoliation (Table 9). Themonitoring site at this location is situated in a corridor of willows that stretches for about onekilometre along Happy Valley Creek. Defoliation of willows was first noticed at the western(downstream) end of this corridor in late December 2009, and as the season progressed, the waveof defoliation spread eastwards (upstream) along the creek. The trees that are monitored wereamongst the last to be defoliated.Willow sawfly population levels at Happy Valley were low throughout the 2008/09 season (Edeet al. 2009) and there was no indication that numbers would increase in 2009/10 as dramaticallyas they did. However, whole tree defoliation has been evident in previous seasons on willows inneighbouring sites particularly on the Ovens River nearby, so willow sawfly populations in thevicinity have been high for the last two seasons. This may explain the increase in numbers at theHappy Valley monitoring site in 2009/10.272.3.2 Willow Tree DefoliationSubstantial whole tree defoliation of willows did not occur at any site until the latter part of theseason, although some limited leaf and branch damage as a result of willow sawfly activity wasobserved during the December assessments at Everton and Kergunyah.The highest levels of tree defoliation across most taxa at Everton were observed in January(Table 9) which followed the peak in willow sawfly number in December (Table 8). Thecanopies of the black willows recovered substantially later in the season. However, there waslittle recovery of crack willow canopies as regrowth was consumed by new generations of willowsawfly. The regrowth of golden willows canopies also remained incomplete for the rest of theseason. The purple osiers were not substantially defoliated by willow sawfly (Table 9) despitehigh willow sawfly numbers in December (Table 8). However, the overall health of these shrubswas not good.At Kergunyah, the foliage present on one tree in January was almost all regrowth, indicating thatfull tree defoliation had occurred prior to the assessment. By March, most of the foliage on alltrees was regrowth. The most severe defoliation was evident in April (Table 9), which followedthe peak in willow sawfly numbers at the site observed in March (Table 8).As described above (Section 2.3.1), whole tree defoliation across the entire Happy Valley Creeksite was first noticed in late December. Defoliation of the trees in the monitoring area was verylimited in January but increased as the season progressed (Table 9). In March, defoliation wasmore apparent on the river-side of the trees monitored than the landward side, but by Aprildefoliation was severe across the entirety of tree canopies.
Page 5 and 6: Table of ContentsSection 1: Managem
Page 7 and 8: 1Section 1: Management Trials1.1 In
Page 9 and 10: willows limit the light which is av
Page 11 and 12: At the Happy Valley and Campaspe Ri
Page 13 and 14: Planting and sowing were undertaken
Page 15 and 16: 91.3 Results1.3.1 Willow Sawfly Pop
Page 17 and 18: 50% - 100% between December 2009 an
Page 19 and 20: The tallest plants at this site in
Page 22 and 23: 161.3.6 Direct Seeding1.3.6.1 Happy
Page 24 and 25: 18Key Points: Willow trees were def
Page 26 and 27: 20B) BrowsingAt both Happy Valley a
Page 28 and 29: 22Plant growth is limited under the
Page 30 and 31: 24Section 2: Monitoring Willow Sawf
Page 34 and 35: 28Table 9: Willow Tree Defoliation
Page 36 and 37: 30Key Points: Willow sawfly populat
Page 38 and 39: 32Section 3: Willow Sawfly Across A
Page 40 and 41: 343.2 Western AustraliaThe first re
Page 42 and 43: 36Appendix 1: Details of Statistica

Willow Sawfly Management Trials - Weeds Australia

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?