Macadamia Quick Decline Caused by Phytophthora tropicalis is Associated with Sap Bleeding, Frass, and Nectria in Hawaii

Macadamia quick decline (MQD) has been a persistent problem since 1986 when it started killing productive 14- to 36-year-old macadamia trees in the Hilo, HI area. Fungi including Nectria regulosa, Xylaria arbuscula, Phellinus gilvus, and Acremonium recifei have been attributed to MQD and could kill twigs on healthy macadamia trees after artificial inoculation (3). The oomycete originally called Phytophthora capsici and later reclassified as P. tropicalis was also considered to be involved in the MQD complex (3). However, the primary causal agent has never been determined and the issue continues to perplex the industry. Between 2005 and 2006, a mature macadamia field on the Waiakea Experiment Station planted with cv. HAES 333 began to experience a high frequency of MQD. Trees exhibiting dull green, yellow, or brown leaves within the tree canopy were observed. Sap bleeding from the trunk, Ambrosia beetles, and Nectria fruiting bodies were consistently associated with MQD. Disease incidence was 22%. Of 21 in...