Black Tree Diseases

The black tree, or black tree fern, looks much like a palm tree. Although classified as a fern, it grows on a single, black trunk and can reach a height of 20 meteres. Native to New Zealand, the black fern tree is not cold hardy and also does not like windy conditions. Like all fern trees, it is also susceptible to a few diseases. Such cases are rare, however, as most established fern trees are quite pest and disease resistant.

Crown Rots

Crown rots are caused by different fungi that infect the top, or crown, of the tree. The spores of the fungus travel on water, so they can spread from plant to plant on wind-borne rain or splashing water. Symptoms of crown rot include deformed and dying fronds. To avoid crown rot, water newly established black tree ferns at the base of the trunk and not from above.

Armillaria Root Rot

This disease is caused by a fungus in the soil, and there is no known cure. The primary symptom is the overall decline of the tree, which will eventually die if infected. If you open the stem or trunk of the tree, you will see the growth of the fungus, which appears as a creamy-white mold. Often, galls (or swollen growths) will appear at the base of the trunk as well.

Phytophthora and Pythium

Phytophthora and Pythium are unusual fungi in that usually infect only mature black fern trees. These fungi live in the soil and invade fern trees at the tips of the roots. Over-watering or poorly draining soil is the primary cause of the growth of these fungi. Because the tips of the roots are the intake area for nutrients and water, the tree will slowly start to die back, starting with the outermost parts of the tree fronds turning brown and moving towards the trunk. A systematic fungicide treatment plan can sometimes prevent these fungal diseases.


Rhizoctonia is another soil-based fungus. Unlike Phytophthora and Pythium, it does not attack the roots. Instead, it attacks the base of the tree. The trunk or stem will rot away, causing young trees to die and mature trees to produce deformed fronds or stunted growth. Like Phytophthora and Pythium, Rhizoctonia can sometimes be prevented if a systematic treatment with fungicides is followed.

Keywords: black tree diseases, Cyathea medullaris, tree fern

About this Author

April Sanders has been a writer and educator for 11 years. She is a published curriculum writer and has provided academic content for several subscription databases. Sanders holds a Bachelor of Arts degree in social psychology and a Master's degree in information sciences and technology.