Parasites BALL MOSS
Jerral Johnson, Associate Department Head and Program Leader for Extension Plant Pathology
Texas Cooperative Extension
Ball moss is an epiphyte. It is capable of manufacturing its own food from nutrients and moisture taken from the air. Unlike mistletoe, it does not derive its food from the host. Although often associated with plants that are in an advance stage of decline, it is not the cause of the decline. In some areas, the moss becomes so dense, that it possibly is restricting normal bud development. Although spread is somewhat restricted, the area of the state where the moss is found continues to expand. Roughly ball moss is found within the area formed by drawing a line from Del Rio to Fredericksburg to College Station to Bay City to Corpus Christi and back to Del Rio.
Small seed are produced in a capsule on a slender 3-5 inch stalk. The stalk extends above the bunchy plant growth. When mature the capsule opens and seed are released into the air. They are carried by air currents until they contact the rough bark of the tree. The seed stick onto the surface and germinate. As the plant grows, root like structures attach the young plant to the rough surface. In the case of a tree this is the older bark. Although the structures extend down into the bark, they are not true roots. They are called 'hold fasts'. Although ball moss will attach itself to many different rough surfaces, property owners are most concerned about shade trees.
Control: Ball moss is controlled with foliar applications of Kocide DF, Blue Shield and Champion are approved by the Environmental Protection Agency (EPA). These products are most effective when applied in late winter. The time between February and mid May is suggested as the best period for treatment. A rain following treatment application is necessary for maximum effectiveness. It is speculated that the moss quickly takes in nutrients through its leaf like structures following rain or heavy dew. When evaluating the copper fungicides as a control for ball moss, an application was observed to remain on the tree for 7 months before significant rain occurred. Soon after that the moss was observed to die. Retreating is suggested if the trees are heavily infested. This is necessary because of the difficulty in getting complete coverage. It is suggested that the copper be applied at the rate of 4-6 pounds or Kocide DF or similar type product per 100 gallons of water. Spray trees to drip point with the spray directed at the moss infested limbs. Within a few months the moss will have a dry, gray unthrifty appearance. It be several months after the application, before the moss will begin to fall from the tree. The hold fasts will have to decay sufficiently to release the moss from the bark. Strong windstorms can decrease the time required for removal of the moss following its death.
Copper is a heavy metal and possibly acts as a poison that blocks the normal biochemical functions. Copper can cause foliage burn to some plants and should be used with caution around plants not listed on the label. Peach, plum, apricot and nectarine in leaf are especially susceptible to injury from spray drift. Apples and pears are not affected by the copper fungicides. Kocide and the other copper hydroxide fungicides are frequently recommended for the control of fire blight on pear and apple trees. The fungicides are approved on a local needs registration in the southeastern United States for the control of certain pecan diseases. A second concern is that spray drift can temporarily stain structures a light blue. Use precaution when applying the copper sprays. Spray on days when the wind is blowing away from sensitive areas. It will wash off when exposed to frequent rain.
Mechanical removal has been used successfully. However, new plants are quickly as new seed land on the limbs. Safety is also a concern, moss is present on many of the small limbs and branches of a tree. This creates an unsafe condition when trying to remove the moss.
LICHENS
Lichens are an example of a symbiotic relationship between algae and certain fungi. They are capable of producing their own food. The algae associated with the fungus is a green or blue-green alga. There are three forms of lichens based on growth patterns. Crustose are species that are closely pressed against the surface of the limb or trunk of dead or live trees. Foliose forms are leaf like or prostrate but are also tightly attached to the tree. Fruticose forms are bush like, erect or hanging. Although lichens are found in most areas of Texas, they are most noticeable in areas that have extended periods of high humidity.
The effect of lichens on a tree are only slightly detrimental. The plants are epiphytes. That is they derive their nutrients from the air and not from the plant on which they are growing. Although they are not parasitized, literature reports suggest that lichens do have a slight negative effect. The main concern is that lichens give a tree an unkept appearance. Presence of lichens also is a good indicator of a thin tree canopy. This often leads homeowners to conclude that lichens are the cause and not the effect of thin foliage. The best control for lichens is maintain the tree in good condition. This will insure a dense canopy which will shade the limbs and reduce photosynthesis. Without photosynthesis, lichens are not able to manufacture food needed for growth and development.
Copper containing fungicides are suggested as possible controls for lichens. Applications of Kocide DF for the control of ball moss, have been observed to control lichens for a short period of time. Currently copper fungicides are not approved for lichen control. Because of their limited affect on a plant, chemical control is not suggested.
MISTLETOE: PEST OR NUISANCE
Mistletoe is an important part of the holiday season. Branches are frequently hung over the door as part of the celebration. Many a young girl or boy received their first kiss while standing under the mistletoe. Unfortunately that is the only good use for this plant. For the rest of the year homeowners are concerned about how to rid their trees of this pest. Although it is a green plant and manufactures its own food, it is a parasite. Water and nutrients needed by mistletoe for its growth and development are taken from the tree's sap. The plant is present on the tree 12 months of the year, but property owners become more concerned about controlling the parasite during the winter months. During this time the leaves have shed from the tree and it is more noticeable. Species of Phoradendron (which means tree thief in Greek) are the leafy mistletoes found in Texas. The European leafy mistletoe species is Viscum album but is not found in Texas.
Mistletoe produces a white berry that is part of many bird's diet. The seed are covered with a sticky substance. They are spread by birds to other trees and deposited on limbs in their excrement. The gelatinous coating acts like a glue to bind the seed to the limb until it germinates. After germination, a root like structure penetrates the bark and grows into the xylem, water conducting tissue of the limb. The root like structures ( haustoria) take materials needed by the mistletoe. Mistletoe seldom kills a tree outright, but heavily infested limbs are stressed. This can increase a tree's susceptibility to other problems.
Small infested limbs can be removed by pruning. This is one of the more effective control methods. Cut limbs at least 12 inches below the mistletoe. Cuts that are made immediately below the stem of the mistletoe, may leave some of the root system. The remaining haustoria will develop a new top. Mistletoe also grows on large limbs or the tree's trunk. When growing on a large limb or trunk, remove only the mistletoe. Do not try to scoop out a portion of the host when removing the plant. If a portion of the wood is removed in an attempt to remove the mistletoe roots, the structure of the limb or trunk is weakened and is more susceptible to breakage due to wind or ice accumulation during the winter months. Wood rotting and canker fungi use the cut as an entry point.
There have been reports that covering the plant with a black plastic bag for 1-2 years was an effective control for the plant. This has the same effect as trying to grow a green plant without sunlight.. Chlorophyll and sunlight are necessary to the manufacture of food for the mistletoe. If this technique is to be effective, the plastic would have to be tightly wrapped and sealed to prevent sunlight from reaching the mistletoe. On small trees with limited infestation, this technique might be used safely. On large trees, unless special lift equipment is available, it would be difficult to wrap the limbs. The presence of the black plastic wraps detract from the appearance of the tree.
Because of the close relationship between the mistletoe's haustoria and the tree's vascular system, chemical control has not been effective. Herbicides such as Round Up, 2,4 D, Paraquat, MSMA and DSMA evaluated in field trials conducted by members of the Texas Agricultural Extension have been ineffective or caused injury to the tree. Currently no herbicide is recommended for mistletoe control.
In the last few years a commercial product, Florel was approved by the Environmental Protection Agency (EPA) for mistletoe control. The active ingredient is an ethylene compound and is manufactured by Rhone Poulenc. Ethylene is a natural occurring plant hormone that increases during fruit ripening. It is labeled for several uses in production agriculture and on ornamentals. Florel is applied during the winter months. When used in the field, Florel kills the top but by late summer new growth is observed breaking through the bark of the limb. Another concern with Florel is that some plants exposed to the drift may experience leaf shedding. However, it has not killed plants exposed to spray drift.
Berries are produced only on mature plants. It normally takes 2-3 years for a plant to reach maturity. By removing the mistletoe plant before it reaches maturity, seed are not produced. This would reduce the spread of the plant. This approach is only effective if all property owners are willing to participate by removing mistletoe from their trees.
Trees vary in susceptibility to the parasite. Cedar and juniper are not bothered by this plant and pecan, live oak and magnolia trees are seldom infected with mistletoe. Water oak, Spanish oak, elm and hackberry trees are frequently observed to be infested. When selecting a tree for the landscape, check with the local arborists, nursery or County Extension Agent for trees that are adapted to your area and do not have a major problem with mistletoe.
To answer the question is mistletoe a pest or nuisance? It is a parasite and its presence is one more stress factor that a tree must overcome. However, it is not a plant that must be removed for most trees to survive, removal is suggested if it can done safely and economically.
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