Bill Pramuk
Trees and People

Bill, I read your article about “Lichens on Trees” dated 8/2/08.  My orange tree has what appears to be the type of hanging moss you described in your article but isn't really Spanish moss.

My question is, is there a safe treatment to kill the moss that will not damage my orange tree? I bought some moss killer for trees/shrubs/walls, etc. but it doesn't say it can be used on citrus. -- A.C.

Dear A.C., Lacking information on your location and a description or photo of the “hanging moss,” I'll answer as best I can.

I wonder if your tree has colonies of “lace” or  ”fishnet” lichen or one of the other pendulous true lichens. If you are in a region like the southern U.S., you might be mistaken and actually have Spanish moss. It is even possible it is a mistletoe. 

First, don't apply any spray materials in a way that is not recommended on the label.

True mosses do not hang from branches. They form compact mats on well-shaded branch surfaces. They are not parasitic.

Regarding lichens, I refer to the little introductory book, “A CALS Mini Guide to Some Common California Lichens” (Janet and Richard Doell, California Lichen Society, available through the California Native Plant Society). It shows three species of pendulous fruticose lichens. Each has a distinctive structure and color, but they all hang vertically, more or less like straight hair. They are not parasitic. Lichens tend to thrive in bright light and clean, moist air. Many are very sensitive and easily damaged or killed by air pollution.

Spanish moss (Tillandsia usneoides) grows in warm climates from Florida to Texas and south to Argentina, but not in California at all, as far as I know. This an an epiphyte in the Bromeliad family. It, too, grows on trees  but is not a parasite.

Mosses, lichens and Spanish moss take nothing directly from the tree, but they might incidentally block light that the tree needs for photosynthesis. 

I sometimes see lichens growing and increasing in trees that are losing vigor, where the canopies are becoming more sparse and open. The canopy of foliage and branches in your orange tree must be sparse and open if it is allowing space and light for large amounts of hanging lichen to grow. A healthy and properly pruned orange tree should be fairly dense.    I suspect that the tree is in poor health for some reason or has been pruned excessively.

Mistletoe, which I've discussed in recent columns, is a parasitic plant. It has a tough stem and root-like structures that actually embed themselves into the stems of the host tree.

The species most common around Napa is Phoradendron villosum, known as oak mistletoe or Pacific mistletoe. It tends to form globe-shaped masses. Sometimes the masses become pendulous when they are quite large. Another species, Colorado desert mistletoe (P. macrophyllum and other botanical names) has been found in Napa County by Jake Rugyt. That species grows from the underside of the host tree branches and hangs downward. I discussed mistletoe control in the two previous columns, so I won’t go into it here.

Rather than spraying anything, I recommend that you first make a positive identification of the plant. Your local county agriculture commissioner's office or or an ISA Certified Arborist should be able to help.

If it turns out to be a mistletoe, you can find the control methods I described in my column Mistletoe Thrives in a Monoculture (April 11, 2009 http://www.napavalleyregister.com/articles/2009/04/11/home/bill_pramuk/doc49e01827285e6718469267.txt).

If the plant is true Spanish moss or a lichen, you could pull it out of the canopy with a pole saw, being careful not to wound your tree. This might help to allow light to diffuse through the canopy.

More importantly, if the tree does look sparse and weak, it should be checked for stress factors, pests and diseases that might have contributed to a loss of vitality. These could include drought stress, root zone disturbances, poor drainage, excessive irrigation, oak root fungus and numerous other possible problems.

Quite often, solving tree problems up in the canopy requires getting to the root of it.

Note to readers: As it turns out, after composing this column, I spoke with A.C. She lives in Port Orange, Fla. The “hanging moss” is a lichen, which is thriving in the clean, humid air.

Following up on the recent mistletoe discussion, I spoke with consulting arborist John Lichter, who co-wrote the study I mentioned. He added that the 10 percent Florel used in the study was a professional grade concentration, which is no longer available. The pruning paint they used to treat the mistletoe stubs was the commonly available black emulsion tree wound dressing sold in garden centers.

Bill Pramuk is a registered consulting arborist. Visit his Web site, www.billpramuk.com, e-mail questions to info@billpramuk.com or call him at 226-2884.