Assessing vulnerable areas for Puccinia psidii (eucalyptus rust) in Australia Trevor H. Booth & Tom Jovanovic Received: 26 January 2012 / Accepted: 17 February 2012 / Published online: 13 April 2012 # Australasian Plant Pathology Society Inc. 2012 Abstract This research note describes a model prepared before the arrival of Puccinia psidii in Australia that identi- fies areas where the rust disease may be most likely to occur . The initial spread of P. psidii since April 2010 has corre- sponded well with the highly vulnerable areas identified in eastern coastal Australia. Keywords Puccinia psidii . Uredo rangelii . Myrtaceae . Guava rust . Myrtle rust Introduction Puccinia psidii Winter, which causes both guava rust and eucalypt rust, poses major threats to many myrtaceous spe- cies in Australia (Carnegie and Lidbetter 2012). Glen et al. (2007) reviewed the taxonomy, biology, impact and options for control of P. psidii and their paper is the fifth most highly read paper from Australasian Plant Pathology (based on number of downloads) over the last three years. Interest in the species has increased with the arrival in Australia of an exotic myrtaceous rust, described initially as Uredo rangelii (myrtle rust), which was detected on 22 April 2010 (Carnegie et al. 2010). Carnegie and Cooper (2011) later proposed that ‘the introduced rust in Australia with tonsured urediniospores should be referred to as P. psidii sensu lato, that the common name ‘myrtle rust’ be discontinued, and that the rust in Aus- tralia be recognised as a member of the eucalyptus/guava rust complex’. P. psidii originated in Central and South America (Glen et al. 2007), though whether the pathotype found in Australia was introduced from Hawaii, the mainland United States (e.g. California or Florida), Central America or South America is uncertain. The Glen et al. (2007) review paper included as their Fig. 4 a map prepared by Booth and Jovanovic identifying areas climatically suitable for P. psidii. Cannon (2009), Carnegie et al. (2010) and Carnegie and Lidbetter (2012) have also mentioned this climatic analysis, but the method used to produce the map has never been published. The purpose of this short research note is to describe that meth- od, so that readers of these papers can understand the cal- culations used. Following the arrival of P. psidii in Australia considerable efforts have been made to determine the char- acteristics of the particular pathotype and develop improved mapping of vulnerable areas. We would expect these more recent studies, which include controlled environment ger- mination studies with the Australian pathotype, will produce more accurate maps of vulnerable areas. But understanding why these maps differ from the map included in Glen et al. (2007) will help to inform future risk assessment, including the possibility that there may be a number of P. psidii pathotypes or strains with somewhat different characteristics (Loope 2011). Methods A simple program called RISK was developed using month- ly mean data for maximum temperature, minimum temper- ature, precipitation and evaporation for 11 333 locations in a quarter degree grid across Australia. These data had been T. H. Booth (*) CSIRO Ecosystem Sciences and CSIRO Climate Adaptation Flagship, GPO Box 1700, Canberra ACT 2601, Australia e-mail: Trevor.Booth@csiro.com T. Jovanovic CSIRO Ecosystem Sciences, GPO Box 1700, Canberra ACT 2601, Australia Australasian Plant Pathol. (2012) 41:425–429 DOI 10.1007/s13313-012-0130-x