A new beetle/fungal complex was recently detected on avocado and other host plants in Los Angeles, Orange, San Bernardino, and San Diego Counties. Photo shows symptoms to look for on the trees.
The two fungal species are Fusarium euwallaceae and Graphium sp., which form a
symbiotic relationship with a recently discovered beetle that is
commonly known as the polyphagous shot hole borer (PSHB, Euwallacea sp.)
(Fig. A). Together, they cause the disease Fusarium dieback (FD). When
the beetle burrows into the tree, it inoculates the host plant with the
fungus (Fig. D), which is carried in its mouthparts in a structure
called mycangia. The fungus attacks the vascular tissue of the tree,
blocking the transport of water and nutrients from the roots to the rest
of the tree, and eventually causing branch dieback. The beetle larvae
live in galleries within the tree and feed on the fungus. FD has been
observed on more than 110 different plant species in California,
including many species common in urban landscapes and on such
agriculturally important species as avocado, olive and persimmon.”
From Akif Eskalen PhD, UC Riverside www.eskalenlab.ucr.edu