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Fusicolla Orange Slime on Trees

Infrequently in the spring, you might see an orange, slimy substance slowly oozing from a wound on a hardwood tree. This is a fungus or a complex of fungi and yeast that colonize the sap that leaks from a tree wound. The primary fungus involved that gives this slime its orange color is Fusicolla merismoides (formerly called Fusarium merismoides).

This old dogwood in Tennessee had major branches that died and were pruned. The leaking sap from the pruning wound became colonized with Fusicolla orange slime, which began running down the trunk.

This old dogwood in Tennessee had major branches that died and were pruned. The leaking sap from the pruning wound became colonized with Fusicolla orange slime, which began running down the trunk.
Photo courtesy of Dr. Alan Windham, University of Tennessee

Here is a close up of the pruned limb, and as the sap was rising in spring, the fungus colonized the leaking sugary sap.

Here is a close up of the pruned limb, and as the sap was rising in spring, the fungus colonized the leaking sugary sap.
Photo courtesy of Dr. Alan Windham, University of Tennessee.

Fusicolla orange slime flow is beginning from a wound on a river birch tree growing at the State Botanical Garden in Clemson.

Fusicolla orange slime flow is beginning from a wound on a river birch tree growing at the State Botanical Garden in Clemson.
Joey Williamson, ©2020 HGIC, Clemson Extension.

Although this slime looks rather disgusting coming from your prize hardwood tree, it is actually harmless. It is very similar to wetwood or slime flux, which are caused by either bacteria or both bacteria and yeasts. The orange slime fungi are simply growing on the carbohydrates (sugars) and moisture in the sap, but they do not cause diseases of the tree’s wood or foliage. These fungi thrive in the spring as the sap is rising and leaking from wounds on tree trunks or limbs.

During March of this year, a river birch at the State Botanical Garden in Clemson was found with a minor sap infection of Fusicolla orange slime.

At least the color was Clemson orange!

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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