For:
By: Daniel E. Mullins
Extension Horticulture Agent
Some “Plant Problems”
Aren’t Problems
Sometimes what seems to be an obvious pest on a plant is often not. The “Big 3” or the most common of these mistaken identities are resurrection fern, Spanish moss and lichens.
Resurrection fern grows on the surface of rough barked trees such as oak and pecan. It is a true fern, with fronds that are about 6 inches long. Though it attaches to tree trunks and branches it is an epiphyte or “air plant,” obtaining no nutrients from trees.
During dry conditions resurrection fern changes to a gray color and curls up as if dead. As soon as moisture returns the fronds uncurl, become green again and return to their original shape. The remarkable ability of resurrection fern to seemingly return from being dead is the reason that this plant was given its name.
Homeowners sometimes believe that resurrection ferns infest and kill trees. Since the fern is not a parasite, this is an unfair assumption. Ironically, the fern is sometimes seen to multiply on an older oak or pecan tree that is in decline for other reasons, and it naturally receives the blame.
Spanish moss is another epiphyte that is often seen hanging from the branches of trees, especially on sites near the coast. It is also an air plant that is only using the tree branches for support.
This unusual plant is in the pineapple family, but unlike pineapple it obtains its nutrients from dust particles and from nutrients that are washed from the surface of branches during rains.
Spanish
moss is rarely a problem and moss laden trees add to the charm and character of
the
Lichens, those gray, scaly or hairy structures seen on shrubs and trees also get blamed for weakening or killing many plants. Like the other two, lichens obtain no nutrients from the plants that they are on.
Lichens have two requirements in order to become well established: bright light and a non-moving surface. Since these same lichen species are found on rocks, fence posts and other non-living structures, they are obviously not plant parasites.
So, why do so many lichen covered plants continue to decline or die? Those that become heavily infested are struggling, weakened plants due to other factors. Once a plant stops growing, which provides a non-moving surface, and loses leaves allowing direct sunlight to strike the branches, then both requirements for the proliferation of lichens has been met.
Rather than blaming lichens for killing shrubs, the gardener should determine the reason that the plants are stressed and make corrections. Sometimes some fertilizer and water is all that is needed.
More often we find that lichen infested shrubs have been established in areas where they cannot tolerate the light and soil moisture levels that are present. For example, Azaleas planted in full sun, or in areas with a hot, Western exposure are sure to become covered with lichens. This is because azaleas are shade loving plants and do not grow well when exposed to direct sunlight.
Excessive lichen growth is also seen on shrubs established on excessively wet sites. Areas with constantly water saturated soils or with a high water table result in limited root systems and associated poor top growth. These thinning, stunted shrubs are home sweet home for several forms of lichens.
Though
resurrection fern, Spanish moss and lichens sometimes cause alarm among
homeowners and gardeners, any damage that they do is minimal. In most cases, control measures should be
limited to growing healthy plants.
Chemical treatments are sometimes used, but are feasible only on rare
occasions.