Round Rock Leader
Saturday, February 5, 2005
By Emsud Horozovic, City of Round Rock Forestry Manager
A couple of community leaders who I like and respect a lot, recently called me and asked for advice on dealing with ball moss and mistletoe. Since those problems are not reserved only for the trees of the town’s leaders, I’m sharing this information with you.
Ball moss (Tillandsia recurvata) commonly grows on trees, fences, and utility wires. It is not a true moss; it’s related to pineapple and ornamental bromeliads. However, it does not taste like pineapple at all (according to some Aggies).
Ball moss is an epiphyte, which means that it grows on other plants but does not take nutrients from them. The “hold fasts” or “pseudo roots” of ball moss anchor it to the surface on which it grows. Unlike true roots, the false roots do not take up water and nutrients. The leaves and stems of ball moss, like those of other bromeliads, absorb water and nutrients from the air. This characteristic has earned bromeliads the nickname of “air plants.”
Ball moss grows well in areas with low light intensity, low air movement, and high relative humidity. Such conditions are found under the canopy of many shade trees. In central Texas, ball moss is most commonly found on live oak trees. Ball moss is spread by windblown seed.
Ball moss is typically found on the lower tree branches that have died due to shading. Homeowners do not need to become concerned at seeing prolific growth of ball moss on a declining tree. Ball moss is not “killing” the tree as it is not a parasite and it does not take nutrients from the tree on which it is growing. However it may stress a tree by smothering emerging buds by reducing the tree’s food making ability.
Some experts believe that heavy infestations of ball moss could cause shading of lower limbs or reduced production of new shoots. These are areas of minor concern. The most significant effects of ball moss on landscape trees are cosmetic.
The decision to control ball moss depends on the homeowner’s personal taste and whether or not control warrants the effort and expense. One way to manage ball moss is by mechanical removal. This can be done manually or with a high-pressure cold water spray. Manual removal is tedious and labor intensive and may be dangerous or impossible without the use of a cherry picker
If spraying, a mixture of ½ pound of baking soda to 1 gallon of water and a surfactant may be used. Copper-containing fungicides can also kill ball moss. Kocide® 101, 4.5LF, DF, and 2000 are copper-containing fungicides currently labeled for ball moss management on live oak and pecan trees. On live oaks, the optimum application time is in February after the old leaves have fallen and before the new leaves emerge. Otherwise, fungicide should be applied between February and mid-May when ball moss is actively growing. Kocide® may be injurious to ornamentals grown underneath the sprayed trees, and the product may react with metal surfaces such as automobiles, lawn furniture and metal roofing. Copper fungicides will leave a blue stain on surfaces they contact, so use care when spraying near buildings, concrete driveways, sidewalks or other surfaces as they will turn blue!
When using a copper fungicide it may take years for the ball moss to fall off as the fungicide inhibits its decay.
Mistletoe: the Christmas kissing plant. A poisonous kissing plant. Kinda pretty with glossy leaves and white berries.
Mistletoe is not usually a serious tree pest, so don’t kiss your tree good-by if it is infected with mistletoe. When heavy infectation occurs, the mistletoe becomes an additional stress factor to the tree and may contribute to poor tree health. It is unlikely that mistletoe kills trees directly, but tree branches may die as a result of mistletoe infection. Effective control of mistletoe is difficult to achieve.
American mistletoe (genus Phoradendron) is a persistent, evergreen, seed-producing plant that is parasitic on certain woody plants, primarily hardwood or broadleaf trees. It is particularly conspicuous on hardwoods after leaf fall. Chinese pistache, crape myrtles, golden raintree, persimmon, sycamore, and conifers are somewhat resistant to mistletoe. The mistletoe derives water and mineral nutrients from the sap of its host. Because the leaves of the mistletoe plant contain chlorophyll, the plant can produce its own food through photosynthesis using water and minerals derived from the tree that supports it. The plant requires direct sunlight for best development. Mistletoe may change from green to a greenish-yellow color during the winter months, but this is not an indication that the plant is unhealthy.
The best indication of mistletoe infection is the presence of dense clusters of vegetation in the crown of host trees. Trees vary in their susceptibility to mistletoe. In Round Rock you’ll see mistletoe mainly in cedar elms and hackberries.
Mistletoe is a dioecious plant -- that is, male and female flowers are borne on separate plants. The flowers are small and creamy-white in color. Only the female flowers produce seeds, which are white and embedded in a sticky, gelatinous pulp enabling the seeds to adhere to the bark of trees. The seeds are commonly distributed by sticking to the beaks and feet of birds or by bird droppings after passing through the bird’s digestive system. Under favorable temperature and moisture conditions, the seeds germinate on the thin bark of small branches. Successful infection of a host tree occurs when the mistletoe seed germinates and a root-like structure called haustoria penetrates the bark. It is common for the tree branch to swell where the mistletoe plant attaches to the branch.
Mistletoe has few natural enemies, and effective control is very difficult to achieve. Destruction of the aerial portion of the plant usually stimulates the development of dormant buds and multiplies the presence of the plant on its host. Where feasible, the homeowner can take steps to minimize mistletoe problems in trees.
Mistletoe plants mature in two to three years, so mechanically removing the aerial portion of the plant before it matures and produces seeds can be of some benefit. Small, infested limbs can be removed by pruning, if they can be reached. Mechanical removal of the aerial portion of the plant on large limbs may also be helpful. Removing part of the wood where the mistletoe attaches to its host should be avoided as this usually causes more damage than the mistletoe itself. Keep in mind that mechanical removal must be done repeatedly because new sprouts will grow from the mistletoe imbedded in the wood of the host tree. Mechanical removal is suggested only if it can be done safely and economically.
In theory, covering the aerial portion of the plant, or its point of attachment after it has been removed, with black plastic (or other suitable material) would block sunlight and the plant would eventually die. However, applying black plastic high in the top of a tree can be difficult and dangerous. In addition, plastic tends to deteriorate over time; and would be unsightly, especially in the winter months when trees are bare. I also recommend using pruning paint on the cuts of mistletoe to stop reproduction and regrowth. It’ll slow that sucker down.
Applying a herbicide to the mistletoe during the winter when the host tree has no leaves has met with limited success. However, because it is so easy to damage the host tree and other nearby plants, using a herbicide is not recommended.
A plant growth regulator called ethephon (Florel® Fruit Eliminator) is the only product registered for the control of mistletoe on deciduous trees. Daytime temperatures should be over 60ºF, the tree should be in its dormant stage, and individual bunches of mistletoe should be sprayed, not the entire tree. The mistletoe will not be killed, but you will not need to retreat for about four years.
So, what do you do with mistletoe? Enjoy it, because you probably won’t be able to successfully eliminate it from your tree. Try to get your sweetheart to stand with you under a mistletoe-infected tree, and steal a kiss!
Credit given to Texas A&M and Texas Forest Service literature.
Forestry Manager Emsud Horozovic