Tree Fern Diseases

Written by david degnan
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Tree Fern Diseases
Tree ferns have dramatic foliage that is prized for gardens. (huge fern tree silhouette image by kubais from

Found in temperate rainforests and tropical areas, tree ferns belong to the order Cyatheales, which includes eight families, 15 genera and hundreds of species. Sometimes used in landscaping, tree ferns are tall plants resembling palm trees in form but with soft, fernlike fronds. Like many moisture-loving plants, they are susceptible to a variety of diseases and pests, but most are easy to prevent and treat.

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Obscure Mealybug

Although technically a pest, obscure mealybugs (Pseudococcus viburni) can cause serious damage to tree ferns. Only female obscure mealybugs feed on plants, attaching themselves to the roots and other tender areas as they extract the plant juices. A powdery, waxlike substance is secreted in order to protect the insect as it feeds. Although they are small, early signs of an infestation are obvious and include chlorosis (yellowing of the leaves), leaf loss and ant infestations. Ants are common indicators of a mealybug problem, since they maintain a symbiotic relationship with them. Since tree ferns are sensitive to chemicals, biological agents like ladybirds are recommended to treat mealybug infestations.


One of the most devastating fungal pathogens known to effect tree ferns is rhizoctonia. Typically soil-borne, it can become dried out and airborne, settling on moist plants and multiplying. It strikes during the summer months when humidity is high, whether from natural or greenhouse moisture. Infection occurs quickly and can irreparably harm a tree fern before showing serious symptoms. Early symptoms include leaf spot, root cankers and pale, wilted fronds. Prevention is the best way to avoid the disease. Use sterilised potting medium and keep potted tree ferns off the ground. If an infection occurs, use a fungicide such as Medallion 50W.


Oedema is a common noncommunicable disease known to effect tree ferns. It occurs most frequently in cool, moist climates where plants absorb more water through their roots than they are able to transpire. Since tree ferns require an environment conducive to oedema, they are particularly susceptible to it. In addition to environmental causes, it can be induced through exposure to certain chemical agents, which will prompt the plant to retain excess water in order to protect itself. Symptoms in tree ferns include small brown cankers or blisters that appear on the undersides of the fronds or along the trunk. Watery, enlarged sores can appear along the soil line and are a sign of an advanced infection. To prevent oedema, tree ferns should be watered sparingly during humid weather and air circulation should be increased, if possible.

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