Willow Sawfly Management Trials - Weeds Australia

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Willow Sawfly Management Trials - Weeds Australia

343.2 Western AustraliaThe first report of willow sawfly in WA was received from Albany in March 2009 (Ede et al.2009) where weeping willow trees had been defoliated at a suburban property. A second report,this time from Bunbury, was also of willow sawfly defoliation of weeping willows in a suburbanbackyard.These two reports prompted a visit to southern WA by Fiona Ede and Valerie Caron in February2010. Several sites from Perth to Albany, and across to Bunbury were assessed for willow sawflywith the insect being found at all but three sites (Fig. 2). Populations were at low levels at mostsites.However, at three sites willow sawfly populations were high. These included the Albany sitewhere willow sawfly had once again defoliated the weeping willows, with the first defoliationevent for the season occurring in mid-December 2009. At the time of the site visit in February,the extent of tree defoliation was assessed at 80%.In addition to the trees affected at this property, willow sawfly defoliation was evident on severalwillow trees at a nearby park, with the extent of defoliation ranging from >90% on goldenupright willows (S. alba var. vitellina) to 40% on other willows (taxon unknown).The second site with high populations of willow sawfly was a park at Cowaramup, which is justnorth of Margaret River. At this site, willow sawfly was present on several tortured willows (S.matsudana ‘Tortuosa’), with 69 larvae found during 5 minute counts. Low levels of twigdefoliation were obvious, but whole tree defoliation was not yet apparent.The third site with high levels of willow sawfly was the backyard in Bunbury where treedefoliation had occurred for the second season, in early December 2009. Willow sawfly numberswere low at the time of the site visit, but the trees were still about 60% defoliated. While willowsawfly populations at this site have been high in both the 2008/09 and 2009/10 season, there havebeen no other reports of tree defoliation in other parts of Bunbury and two additional sites whichwere checked in February 2010 for willow sawfly had only very low populations.If the experience of willow sawfly in south eastern Australia is repeated in WA, it is likely thatwillow sawfly will continue to expand its range to all areas with willows over coming seasons. Itis also likely that populations will increase at some sites to the level required to cause whole treedefoliation and this may be extensive in some parts of the landscape. However, willow sawfly isunlikely to cause large scale willow tree death across WA.Key Points: Willow sawfly is widely distributed across south eastern Australia; Willow sawfly is now present at several sites in south western WA, and hascaused whole tree defoliation of willows at sites in Albany and Bunbury.

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