Sugar Volcano

Sugar volcanoes are a tree’s response to boring, disease-carrying insects.


Now, when I say boring, I do not mean dull witted conversationalists. These pests are invasive shot hole borers that chew holes through bark to get at the sugary, nutrient rich sap found in the cambium layer.

Sugar volcano on avocado (UCANR)

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Borers and disease

Borer entry and exit holes, while very tiny (0.03” in diameter) compromise a tree’s outer layer of defense. As the beetles bore into the wood, they carry with them three different species of fungal spores. These fungal spores enter the tree, bringing Fusarium dieback. Fusarium dieback is a fungal disease in which fungi block a tree’s vascular system, halting the flow of water and nutrients. Trees infected with Fusarium dieback must be destroyed and disposed of by a professional arborist.

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Avocados and exudates

Peach, citrus, and pecan are just a few of the more than 200 tree species impacted by this problem, as are grapevines, but the sugar volcano is specific to avocados and box elders.


Exudates are secretions. When an avocado tree is first attacked by shot hole borers and Fusarium dieback, it will respond by pushing a sugary exudate out of the borers’ entry and exit holes. This sugary secretion often includes frass and sawdust. As it dries, this sugary exudate forms a white, crusty ring or cone-shaped patch on the affected branch.


And these crusty white patches, dear readers, are sugar volcanoes.


Now you know.