Walnut blight disease development on Guangxi walnuts

Walnut blight (Xanthomonas arboricola pv. juglandis) disease incidence was estimated on commercial plantings of presumed J. sigillata x Juglans regia hybrids in Guangxi (2013, near harvest; high expected disease pressure) and J. regia, J. sigillata and presumed J. sigillata x J. regia hybrids in Sassafras eastern Australia (2014, near harvest; moderate expected disease pressure). The disease incidence was compared to a model based on rainfall during leafing out developed earlier in Tasmania. The results indicated that in Sassafras the model worked well for J. regia and J. sigillata. However, in both Sassafras and Guangxi the levels of blight observed on the husks of near mature hybrids was well below that expected. These data are a preliminary suggestion that some J. sigillata x J. regia hybrids may contain useful resistance to walnut blight.