Why Do Eucalyptus Drop Their Branches?

Heart/Sap Rot

• Eucalyptus drop their branches when they have been afflicted with an advanced case of heart or sap rot, the product of several fungal diseases that cause severe decay of wood in the tree. In some instances, a eucalyptus may decompose in a short time, ranging from months to years. Older, weakened trees are especially susceptible as these fungi eat away at the center of the branches. It is difficult to view the damage on the surface of the tree unless reproductive fungal bodies are present.

Rot Features

• The reproductive structure is fungal fruiting bodies that grow on the surface of the eucalyptus. Called conks or brackets, these shelf-like structures jut out from the surface of the tree. Other fungi like Armillaria mellea produce mushroom-shaped growths at the base of the eucalyptus that normally appear after a period of heavy rain, typically in the fall or winter. Dead or diseased eucalyptus branches should be cut away and destroyed to prevent the spread of the fungus.

Phytophthora Rot

• Phytophthora root and crown rot caused by several members of the Phytophthora fungal species can damage the eucalyptus tree to the extent that its branches begin to drop to the ground. The first symptom of the disease is the yellowing and premature defoliation of leaves. The fungal attack continues through stems, twigs and branches. In some cases, the tree may die within one year of infection while in other circumstances, the rot may require several years of continued infestation before it is lethal.

Canker

• Canker diseases are brought on by a number of different pathogens. The disease displays as a depressed area full of dead tissue on the stem or branch of a eucalyptus tree. Typically, a collection of raised scar tissue encircles the canker. The discolored, infected bark oozes a toxic resin, and tiny, fruiting bodies may appear on leaves and branches. As water and nutrition is prevented from traveling through the decaying wood, the weakened eucalyptus drop their branches to the ground.