Walnut Blight Sustainable Management Research in New Zealand

Walnut blight Xanthomonas arboricola pathovar juglandis is the most significant pest or disease issue in New Zealand commercial walnut (Juglans regia) production. Typical management has involved selection of less humid regions and copper based sprays. Research in New Zealand has included determining cultivars that show a promise of lower blight susceptibility and investigation of the effect of timing and form of copper sprays. There has been no clear success in the use of adjuvants to improve the efficacy of copper based sprays and no effective alternatives to copper sprays elucidated in research to date. Mankocide had previously demonstrated improved efficacy over Kocide even at lower copper levels. In this research, there was no apparent benefit in incorporating extra Mancozeb with Mankocide to match the copper mole for mole with dithiocarbamate. The use of copper methionine as an alternative form of copper yielded low efficacy on walnut blight. Efficacy of copper sprays was reduced by using copper methionine as a form of copper. Bacteriophages of X. arboricola pv. juglandis have a demonstrated capability of lysing all New Zealand isolates of the pathogen that have been collected in preliminary work. The potential of bacteriophages as a biological control agent is discussed but there is a need for a reliable bioassay to progress research further.