Tree fungus is damaging to trees and typically a sign that a tree is under stress or has been wounded. Tree moss, on the other hand, is not always damaging to trees unless it becomes too thick or heavy. Managing both fungus and moss can be difficult. Fungus, in particular, is best managed with preventative measures such as proper tree care.
Tree fungus lacks chlorophyll and therefore takes its nourishment from other green plants much the way a parasite takes nourishment from a host. This process causes disease in the tree. Fungi can be microscopic. Larger fungus, called wood rotting fungi, produce the large, hard mushroom shaped forms that you might see on trees when hiking in the woods. These fungi can also be quite colorful.
Fungi that invade wounds on a tree are referred to as cankers. Cankers can be both annual or perennial. Annual cankers will be healed over by callus each year. Though they still cause damage to the tree, it is not as severe as perennial cankers. Perennial cankers continue to grow from year to year, spreading to branches and twigs. Cankers are more prevalent in younger trees, but can invade any tree that is experiencing stress or has been wounded.
The best way to prevent fungus from impacting trees around your home or in your garden is to minimize the amount of stress they experience. The most important thing you can do is to make certain trees are planted in locations where they can thrive. Drought, insect infestations and exposure to chemicals can also cause tree stress. Regular, deep watering and controlling for insects with organic methods, whenever possible, will help keep your trees healthy. Remember that cankers invade trees with wounds. Preventing wounds to your tree may be out of your control. Removing dead branches from nearby trees can keep them from damaging your tree when they fall.
Mosses are plants that do not have roots, stems or leaves. They typically grow in areas of high moisture content and can be used as ornamental plants in rock gardens, near ponds and in other shaded garden areas. Mosses that grow on trees can make an interesting, natural feature in your garden. However, you will need to manage tree moss so that vigorous growth does not damage the tree.
Certain types of moss, such as Spanish moss, are considered parasitic. If you are concerned that moss on your tree is harming it by preventing growth or limiting sunlight, removal can usually be done by hand. Moss may also need to be thinned from trees if it becomes too heavy. Moss can hold a large amount of moisture, weighing down tree branches and potentially causing them to break.