Efficacy of cuprous oxide for control of dothistroma needle blight in Pinus radiata plantations in Australia

Dothistroma needle blight (DNB, Dothistroma septosporum) is a significant disease in Pinus radiata plantations on the Northern Tablelands of New South Wales and in the Murray Valley region of Victoria/New South Wales, Australia. Aerial application of copper oxychloride has been used to control DNB in these regions since soon after it was established. Research in New Zealand, however, has identified cuprous oxide as a more efficient and cheaper fungicide for controlling DNB. In this study, we test the efficacy of a single (applied in late October-early November) and double (October and February) application of cuprous oxide for controlling severe (> 50%) DNB in P. radiata plantations on the Northern Tablelands. We established replicated blocks 5-10 ha in size to ensure the results were operationally valid. Disease severity and defoliation were assessed on individual trees pre- and post-treatment, and aerial surveys were conducted to gauge the effect of treatments on the subsequent operational fungicide spray program. Cuprous oxide application significantly (P < 0.01) reduced disease severity compared with no application, with a second application reducing severity even further. Ten months post-treatment, tree-level disease severity was 39% in unsprayed plots, 31% in single-sprayed plots and 8.5% in double-sprayed plots. The double application effectively reduced disease to negligible levels, while the single application provided adequate control for up to three months. At an operational level, even the single fungicide application reduced disease severity at the block scale when mapped during aerial surveys. Based on aerial assessments that trigger control action, all unsprayed plots required fungicide application in the season after the study (2013), while only two of seven single-sprayed blocks and none of the double-sprayed blocks required additional control. Extrapolating from this, a single fungicide application meant that 70% of the area did not require a fungicide application in the subsequent year. Based on these results and evidence from New Zealand, we recommend that cuprous oxide replace copper oxychloride for DNB control in Australia and that a double application is used in areas with severe (> 50%) levels of the disease.