About the Disease

Shoot dieback symptoms on infected castor oil plant. Source: Akif Eskalen, UCANR
Shoot dieback symptoms on infected castor oil plant. Source: Akif Eskalen, UCANR
Fusarium is introduced into its hosts by the beetle. The fungus destroys the food and water conducting systems of the tree, eventually causing stress and dieback. The larvae of the beetles within the beetle gallery in infected trees feed on the fungus, forming a symbiotic relationship between the fungus and beetle.

Fusarium dieback symptoms: White powdery exudate either dry or surrounded by wet discoloration of the outer bark in association with a single beetle exit hole. While there is no visible injury to the bark at this stage of colonization, examination of the cortex and wood under the infested spot bored by the beetle reveals brown discolored necrosis caused by the fungus.

Known fungal species for pest-disease complex associated with PSHB are Fusarium euwallaceae, Graphium euwallaceae and Acremonium pembeum. KSHB carries new species of Fusarium and Graphium.