(Parasitic and Epiphytic Plants)
Ball Moss (plant – Tillandsia recurvata): Ball moss has caused concern among homeowners in the southwest part of Texas for many years. Ball moss is an epiphyte. It grows on the bark of a number of Texas shade trees; live oak, post oak, hackberry, tallow, cedar, and others. It first occurs as small, gray green tufts that develop within a relatively short time into a dense “ball” composed of numerous individual plants. The plants form root-like holdfasts which penetrate into the rough bark of the tree. These holdfasts often completely encircle a limb. Spread is by windblown seeds which are produced on 3 to 4 inch long stalks. The seed are light and are covered with a fluffy material which aids in their movement. Within the last few years, the plant has been spreading eastward from its former Southwest Texas habitat.
The use of the fungicide Kocide 101 at the rate of 4-6 pounds/100 gallons of water will control the plant. Applications should be made in the spring (late February, March or April) just prior to the normal spring rainy season. Kocide applied during dry periods will not be as effective. When ball moss growth is dense, an additional application should be made 12 months later. Generally, no more than two applications are required for control of ball moss depending upon how large an area is sprayed and how many trees are in the area that can serve as a seed source.
Spanish Moss (plant – Tillandsia usneoides): This long, whisker-like plant growth hangs from trees in Southeast and East Texas. It is an epiphyte. It grows on hardwoods and conifers along rivers and creeks in the more humid areas of Texas. It is a member of the pineapple family (Bromeliaceae). It has been reported to kill trees where development is extensive. This seldom occurs. It can be removed using mechanical means where growth becomes thick enough to cause tree damage. Chemical treatments are not recommended.
Mistletoe (parasitic plants – Phorandendron flavescens var. villosum, P. flavescens var. pubescens, P. flavescens var. macrophyllum, P. bulleanumvar. bolleanum, P. bolleanum var. capitellatum, P. juniperinum): Mistletoes are parasitic plants which derive their food from the host plant. In severe cases mistletoe will kill trees. The seeds of mistletoe are borne as white fruit on female plants. These berries are sticky and are spread by birds. The seed germinate and penetrate young, thin bark. As the seed germinate, a haustorium is formed which penetrates the cambium and eventually on into the wood. Infection often causes large swellings to be formed around the point of entry.
Chemical control has not proven satisfactory, even though a large number of chemicals have been evaluated. Physical removal has been used but is only successful if the haustoria are removed. This may mean removing a large portion of the limbs in some trees. Cuts should be made 12 to 18 inches below the area where the mistletoe is attached. A hoe or rake have sometimes been used to brush the plants off the trees, but this gives only short term relief with new growth springing up from the point of attachment.
Lichens: A lichen is a combination of a fungus and a green or blue-green alga enclosed by the fungal hyphae. The fungus obtains food from the alga, which manufactures food through photosynthesis and the alga receives some of its food and protection from the fungus. Three forms of lichens exist – crustose (flat type of growth), foliose (leaf-like but with prostrate growth), and fruticose (bush-like and erect or hanging growth). The effect of lichens on trees is only slightly damaging. Heavy lichen growth indicates poor tree growth as a result of some other cultural problem. Lichens can restrict gas exchange from the limb or twig and can restrict the amount of light received by a limb.
Materials used in the control of ball moss will kill the lichens for a short period. Regrowth usually occurs within the same year after the tree was sprayed. Chemical control of lichens is not currently recommended. This is due to two reasons, one, chemicals are currently not cleared by EPA and control has not been of long enough duration to warrant spraying. Rather, trees should be encouraged to develop a dense canopy which will shade out the lichen growth.