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‘What is that?’

Posted: July 24, 2014 11:32 a.m.
Updated: July 25, 2014 5:00 a.m.

In the quest to answer the many questions I receive about trees, see below for part three in the continuing series.

What is that greenish, fuzzy-looking stuff growing on the tree bark? Will it kill my tree?

That fuzzy stuff my friends, is called lichen (pronounced ‘like-en’). Lichen is sort of a biological wonder really. It is a symbiotic or beneficial relationship between fungus and algae. Their mutual association has evolved so completely they go together like peanut butter and jelly. Lichens grow from the tropics to the polar regions of the Earth, far beyond where trees grow. Lichen can appear in many color variations from green to gray-green, yellow, brown or blackish and take on several forms flat, leaf-like, crust-like, fuzzy or branching. While they grow on many different kinds of trees such as maple, oak and crape myrtle, they do not grow in polluted air.

There has been debate as to whether or not lichens cause harm to trees, but I have never come across any research to confirm any negative effects nor ever seen a tree die because of it. However, some folks firmly believe that lichen do cause harm. This is likely due to the fact that as a tree declines in health and vigor (due to other factors) there is a decline in the leafy canopy. This in turn allows more sunlight to penetrate the branches where lichen grow. Since algae responds to sunlight by increasing in growth, the lichen plant will grow and multiply as well. Its presence on a tree can be associated in proportion to the amount of sunlight it receives. Increasing tree vigor by proper watering and fertilization is one way to slow the growth of lichen. They are not harmful to the plant and are merely using the tree as a place to anchor. Since there is no harm to the tree by lichen’s presence, control measures are not needed.

What is that smelly liquid stuff that leaves a black stain on the tree trunk? Will it kill my tree?

The black stain or oozing fluid that folks most notice running down the tree trunk may appear any time during the growing season. It primarily occurs on oak trees, young, old and in between. Don’t ask me why; it’s just one of those things. The oozing fluid is called slime flux; which is appropriately named due to the mucus-like consistency that slowly flows from a small hole in the trunk.

This condition is known as wetwood and is thought to be caused by a localized bacterial infection in the wood cells under the bark. According to Dr. Alex Shigo a renowned plant pathologist and studier of trees for 30 years (now deceased) says that wetwood is “Wood altered to a higher state of protection against mechanical disruption or decay by pathogens that make the wood so high in moisture, pH and microelements that decay-causing pathogens are not able to infect.”

Over time, the bacteria-infected wood causes the tree sap to ferment resulting in a buildup of pressure inside the tree until it is forced out. Slim flux is relatively harmless but may smell like stale beer or vinegar. Bees, wasps, ants and other insects are attracted to and feed on the sap. Wetwood does not kill the tree, is not contagious to other trees and is not a condition needing any kind of treatment. It will though from time to time, re-appear each year (generally after periods of rain) or it may not show up for several years. It does tend to leave a black stain on the bark, which is unsightly but harmless. I’ve also noticed wetwood in elm trees but not to the same degree as in oaks.

For folks who may be allergic to stinging insects or have small children who may play near a tree with wetwood, a simple way to avoid an incident is to wash away the slim flux with a garden hose spray nozzle. If the area is in a reachable place on the trunk, a mix of sudsy water may be used to wash and rinse it away. Never drill a hole in the infected area to help drain the slim flux as this will puncture internal protection zones within the tree and make matters worse. The good news is, because of the high concentration of pH and low oxygen levels, decay fungi will not live or actively eat away the wood. In a sense, wetwood, while unsightly, is a kind of protection against more serious problems.

What is that stuff hanging on the tree branches? Will it kill my tree?

That stuff is Spanish moss. Spanish moss (Tillandsia usneoides) is a recognizable and signature southern plant but misunderstood by many. To native southerners, these gray-green strands draping from the branches of live oaks and other trees are a natural part of the scenery, while many newcomers fear that it may be killing their trees.

Contrary to popular belief, Spanish moss causes little to no detrimental effect on a tree as it is an epiphyte. Epiphytes are unique in that they grow on other plants without taking any water or nutrients from them and use the host plant for support and protection. Spanish moss can be seen hanging from several types of trees, including pecans, oaks and pines. It is sometimes blamed for tree problems that are caused by other reasons. Increasing tree vigor by proper watering and fertilization is one way to restrict the growth of Spanish moss.

There are no chemical treatments available for its control. However, an abundant crop of moss within the canopy of a tree may lead to the decline of small twigs by shading out the lower leaves of the tree. If this is the case, it can easily be removed by hand and disposed of. Otherwise, enjoy the ambiance it creates in your landscape and appreciate this small native plant as a part of the South’s natural heritage!



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