Michael Womack
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Saturday, January 15, 2000

Tree just epiphytes' hangout

Moss and lichen harmless guests

 

During the months when trees are dormant, many homeowners become more aware of plants growing on their trees. The lack of leaves on deciduous trees makes anything growing on the bark or limbs apparent.
   Ball moss and lichens are commonly found in area trees; however, unlike the parasitic mistletoe, they are not taking nutrients from the tree on which they are attached. Ball moss and lichens are epiphytes, or "air plants," only using the tree as a place to live.
   Ball moss (Tillandsia recurvata) has caused concern among homeowners for years. Ball moss is actually a bromeliad and related to not only its kissing cousin, Spanish moss (Tillandsia usneoides), but the pineapple (Ananas sp.) as well. Ball moss grows on the bark of a number of trees, including live oak, hackberry, and tallow.
   No cause of decline
   Spanish moss usually occurs first as small gray green tufts that develop within a relatively short time into dense "balls" comprised of multiple individual plants.
   Ball moss produces light seeds covered with fluffy material on the end of three- to four-inch flower stalks that allow them to be easily dispersed by wind. The seed lands on tree bark or other rough surfaces such as a telephone pole or a brick wall, where it germinates. As it grows, holdfasts, which are not true roots, extend into the bark for support.
   Although the ball moss doesn't derive nutrients from the tree, it is often associated with trees in advanced stages of decline; however, it is not the cause of the decline. In extreme cases, however, it can become so dense that it actually restricts normal bud development.
   Ball moss can be removed manually from trees. In extreme cases, it can also be controlled with foliar applications of Kocide DF, Blue Shield or Champion. These products are most effective when applied between February and mid-May. A rain following treatment application is necessary for maximum effectiveness. Within a few months, the moss will have a dry, gray appearance and it may be several more months before the holdfasts decay and the ball moss begins to fall from the tree.
   Three types of lichens
   Other unsightly residents on tree limbs are lichens, an example of a symbiotic relationship between a certain fungus and a green or blue-green algae. These gray-green crusty organisms grow on the bark of many trees, including oaks and mesquite, but again, they are not parasites. Although lichens are found in most areas of Texas, they are most prevalent in areas with extended periods of high humidity.
   Lichens are classified into three forms based on growth patterns. Crustose are species that are pressed against the surface of the limb or trunk. Foliar forms are leaf-like or prostrated but also tightly attached to the tree, while fruticose forms are bush-like, erect or hanging.
   Lichens are often a good indicator of a thin canopy. Homeowners often conclude incorrectly that the lichens are the cause and not the effect of a thin foliage. The best control for lichens is to maintain the tree in good condition. A thick tree canopy will reduce photosynthesis in the lichens and thus eliminate their food source.
   Chemical control is not suggested due to the limited effect of lichens on tree growth. Copper fungicides as mentioned above are not labeled for lichen control.
   If you see either of these plants on your tree limbs, don't panic. Just remember that these plants are just looking for a place to hang out, not a free meal from your tree.
  

2000 Caller-Times Publishing Company, a Scripps Howard newspaper. All rights reserved.