Question

1-1.jpg   QUESTION: On just one of our oak trees in our backyard, there is a light green scaly fungus that I haven't been able to find online.  It is on the west & NW sides of this one tree (there are numerous oaks around it) and starts at the base and way up the tree.  I've attached a picture.  Whatever this fungus is, it is also growing on the asphalt shingle roof on the porch about 15' away from the tree.  If you can identify it, what should be done about it, if anything.  Thanks.

ANSWER: These are 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.  

The baking soda recommendation I have heard of is 40 pounds of baking soda per 100 gallons which comes to 0.4 lb of baking soda to 1 gal of water. But I would not do anything about the lichens but I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. this will increase the overall health of the tree.

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QUESTION: What does the baking soda treatment do?  Does it get sprayed on the lichens?  Is it normal that it would also grow on an asphalt roof nearby?
Thanks again.

Answer
It kills the lichen --it is sprayed on the lichens on the trunk and branches of the tree.

Moss and lichens are more than a cosmetic issue on many kinds of roofing materials - asphalt shingles, roll roofing, wood shingle roofs, wood shake roofs. By holding moisture against the roof surface lichens but more so moss speed the wear of the asphalt shingle surface in freezing climates by increasing frost damage to the mineral granule coating on the shingles.

Because lichens growing on a roof surface does not have as much thickness of body as moss, it will hold less water on the roof surface and is less of a wear factor than moss.

Therefore if we have only lichens growing on a roof surface we would be less quick to try to clean it off since lichens not only has a tighter "grip" on the roof surface but the cleaning process for lichens risks doing more harm than good to the roof surface.

Lichen does not have roots like most other plants and it can grow without soil. In moist or damp climates lichen flourishes, growing on roofs and walkways and garden walls. Some people feel its lovely silver shading adds color and charm. Admired for its tenacious ability to survive, lichen grows on roofs worldwide. However, if allowed to grow, it may turn black and become visually unattractive. Even though it does not harm the roofing material, homeowners may want to eliminate its presence.

Here are some ways to treat lichens on the roof.


1 Inspect the roof shingles visually. Lichen will build up on the north side of buildings and in areas shaded most of the day.


2 Clean the roof annually. Sweep off dirt, branches and debris and then wash down the roof surface with a garden hose with a pressure nozzle. Cleaning removes materials that trap water on the surface of the roof shingles and delays the drying process. Start at the peak of the roof and work down so as to not drive water under the shingles. To correctly wash a roof you will need to stand at the top of the roof and point the hose downward. Potentially dangerous, roof cleaning should proceed with safety uppermost in mind. Do not attempt to clean steep pitched roofs without adequate safety gear.

3 Mix 1 cup of bio-degradable liquid dishwashing soap and 1 cup powdered oxygen bleach in 5 gallons of water and apply to lichen prone areas with a push broom brush or hand scrubbing brush. Scrub gently. Rinse with clear water. Commercial chemical preparations, though costly, have proven effective. Follow manufacturer's label directions carefully. Purchase lichen and roof stain removal chemical products at building supply and home and garden stores.


4 Enlist the services of a professional roofing contractor to remove excessive lichen build-up on the roof. Roofers have the equipment and experience required to do the job safely.


5 Install zinc strips after cleaning the roof. Zinc will prevent lichen from accumulating. Zinc strips (1/2 inch wide and 2 to 3 inches long), available for purchase from hardware stores and home and garden centers. Attach by nailing along the ridge line of the roof. Strips should be nailed horizontally along the peak of the roof, spacing them about 6 to 8 inches apart. Follow manufactures instructions.


6 Spray patches of lichen with vinegar until thoroughly saturated. An application of vinegar kills lichen. The odor intense odor will quickly disappear as the vinegar dries and evaporates. To remove the lichen, scrub with a firm brush with soapy water. Use an organic liquid soap. A roof scrapping tool (a long handled tool with a flat scrapping blade) can also aid in lichen removal.


7 Apply shingle oil with an airless sprayer. After the shingles are clean and dry, spray with shingle oil to preserve the wood and discourage the growth of fungi, mold, lichen and algae.