Horticulture Hotline 03/18/19
By Bill Lamson-Scribner
Bill,
On the bark of my Crepe Myrtles, I noticed grayish
growth. I can peel this growth off
fairly easily. What is this growth and
is it hurting my tree?
I have been asked some form of this question in Possum’s, on
the radio, and at an oyster roast in the last month. It sounds like you have
lichens. Lichens are grayish-green
organisms that are a cross between fungi and algae. They make their own food and collect their
own water and minerals, so technically they do not harm the plant or tree on
which they are growing.
Since lichens manufacture their own food through
photosynthesis, a healthy actively growing plant or tree is the best defense
against lichens. If the tree or shrub has a thick canopy, the lichens will not
survive since they need sunlight to manufacture their food. Culturally, the
plant must be planted in an area that provides the conditions that the plant
can thrive, so it produces a dense canopy that will shade out the lichens.
Proper fertilization based on soil tests and proper pruning will help to keep
the canopy thick.
Think of trying to grow grass under the thick canopy of a
tree – the grass needs sunlight like the lichens and will not grow in the shade.
Although lichens do not hurt the plant, it could be a sign
that the plant is in a very moist area or in an area that is not getting good
air movement. Any area that is not ideal for plant growth can contribute to
lichen growth. A shady area for Crepe Myrtles will also cause the lichens to
flourish.
Lichens thrive in these conditions which are not very
favorable for plant growth. With our
on-again, off-again rain, it is hard to control these moist conditions. If you have an irrigation system, be sure you
are not over-watering, as this contributes to the problem. Irrigation systems are great; however, if
over used can cause great problems in the landscape. Large patch fungus and lichens could be a
couple of examples of over-watering issues.
The best control for lichens is cultural controls. Try to
minimize the moisture in the soil and maximize air movement around the plants
and trees. Pruning to increase air
movement will help dry the soil.
Excessive mulch whether fallen leaves, pine straw or wood mulch will
keep moisture high in this area and should be limited to 2-3 inches in depth. A
good fertility program derived from a soil test helps a whole bunch.
Lichens, although a bit unsightly, do not harm the plant, so
if you can’t get the moisture out of the area because of large trees, it may be
something you just have to live with.
Mistletoe is a parasitic plant that lives in our trees. It manufactures its own food; however, it has
root-like growth that penetrates the bark and collects minerals and water from
the host tree. If left to grow, it will
eventually kill the host tree. It has seeds
that birds eat and spread. These seeds
also get under the soft bark and germinate spreading the parasitic plant.
Wet fall means fleas. Protect your buddy!
Always read, understand and follow product label. The
product label is a Federal Law.
