Question: What is ball moss and can it kill my tree?

Ball moss commonly occurs in Florida's oak trees. Many decling oaks are frequently inhabited by large numbers of Ball moss. Therefore, the question is frequently asked, "Is Ball moss killing my oak tree?"

First, let's examine the question by discussing, "What is Ball Moss?" Ball moss belongs to the same genus as Spanish moss, Tillandsia usneoides. Ball moss plants are individual tufts of leathery, thread-like curving leaves. The leaves are 1 to 7 inches long covered with silver-gray or brownish scales. The pale violet flowers are borne on short spikes. Ball moss is classified as an epiphyte, a plant attached to another but not growing parasitically upon it. Epiphytes are called air plants because they obtain essential nutrients from air, water, and debris.

Ball moss in large numbers has been suggested to cause decline of their live oak hosts by shading. However, Ball moss colonies tend to concentrate deep within the canopy on main trunks, major branches, or small twigs within the canopy. Located within the canopy, Ball moss causes minimal shading of the host. Declining live oaks usually die back on the periphery of the canopy, and small chlorotic leaves occur throughout the canopy. Live oak twigs completely encircled by the wiry roots of the Ball moss show no bark enlargement which would suggest stem girdling.

Studies show that specific conditions necessary for an epiphyte to reduce the recycling of nutrients would be: (1) the site must be relatively infertile; (2) the nutrients must be easily lost, i.e., leached from the root zone; (3) the woody plants must be suitable hosts; (4) the hosts must be near a seed source of the epiphyte; and (5) sufficient time must pass to permit high numbers of the epiphyte to become established.

The hypothesis of epiphyte nutrient interception causing greater host stress and eventual decline could be overcome with applications of nutrients. Fertilization with the limiting nutrients would release the hosts from any adverse effects of nutrient interception. Fertilized hosts would increase their canopy density, thereby decreasing the epiphyte numbers.

Ball moss does not parasitize live oak, one of its primary hosts. The roots of the Ball moss do not penetrate or remove nutrients directly from the host. Epiphytes such as the Ball moss could increase stress on woody hosts when they are already under stress. The small amount of nutrients possibly intercepted by the epiphytes would not cause healthy hosts to decline. Proper fertilization and care is necessary to produce healthy plants on poor sites.

Ball moss need not be removed from healthy plants. Fertilization of stressed plants, thus stimulating renewed growth, would be more beneficial than removal of the Ball moss. Removal of the Ball moss alone would not appreciably increase plant growth.