Crown damage by the aphid Essigella californica in a Pinus radiata plantation in southern New South Wales: causality and related management issues

Abstract

The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first detected in Australia in 1998 and is now a major damaging agent in Pinus radiata plantations throughout south-eastern Australia. Tree-level crown damage was visually assessed over four years, from 2006 to 2009, in 120 plots located in Green Hills State Forest (Hume Region, Forests NSW). The plots represented 30 tree-age classes and a range of related stocking densities. We applied random forests and linear mixed modelling (ASReml) to examine the relationships between crown damage and a series of silvicultural and local climatic and terrain attributes. Consistent with previous observations, our results showed that crown damage due to E. californica is highly variable and is influenced by a suite of interacting and confounding factors. We identified prevailing climatic conditions, stand age and tree genotype as being the most influential, as well as threshold values associated with these relationships. These predictor variables can be used to stratify plantation planning units according to risk of defoliation by E. californica and for prioritising and targeting management activities such as aerial surveillance, release of the introduced biological control agent Diaeretus essigellae, possible late-age fertiliser application and in the future, the deployment of Essigella-resistant pine genotypes.

Keywords:

• crown
• defoliation
• assessment
• management
• plantations
• Essigella californica
• Pinus radiata
• New South Wales

Acknowledgements

The results presented here arose from a multipurpose study site sponsored by the Cooperative Research Centre for Forestry. Ian Smith, Caroline Mohammed, David Page, Charlma Phillips, Jan Verbesselt, Darius Culvenor and Neil Simms all participated in the Forestry CRC Green Hills SF forest health/remote sensing projects and we acknowledge their assistance in collecting the field data for this study. The authors also thank Charlma Philips for her internal review of the manuscript.