Live oak trees (Quercus virginiana) are evergreen oaks susceptible to a variety of diseases that cause cosmetic injury to severe infection and death. Maintaining your live oak keeps it vigorous and raises resistance to diseases. This is important because many diseases cannot be controlled, and trees as large as the live oak are difficult to treat chemically.
Oak Leaf Blister
Oak leaf blister is an infectious disease caused by the fungus Taphrina caerulescens. Symptoms include blister-like bumps on leaf surfaces that appear lighter in color than the green of the leaf; blisters change from green to brown. The fungus causes excessive growth of leaf tissue, resulting in formation of the blisters. Though milder infections cause minimal damage, a tree can lose its leaves if the case is more serious. Trees become infected during the spring season. If the tree is young and small enough to cover with a fungicide, apply "just before budbreak," recommends the Clemson University Extension. For larger, more established trees, there is no effective treatment.
Oak wilt is a fungal diseases caused by a fungus called Ceratocystis fagacearum. Fungi are spread from one root system to another in live oak trees. Water and nutrients that typically move from the roots to the leaves become halted by the fungal infection, leading to death within two months to a year, according to the Texas Cooperative Extension. Symptoms include a dysfunction called veinal necrosis. In veinal necrosis, the vein systems appear to be vigorous while the tissue surrounding them dies, first turning orange and then brown. For control, vary the trees you plant to prevent spread of disease from one oak to the next, prune live oak trees either during the winter months or late summer, and cover any wound with pruning paint. For infected trees, apply a fungicide with the main ingredient propiconazole.
Spanish moss (Tillandsia usneoides) is a live oak disease known as an epiphyte, or an organism that inhabits the surface of a plant, relying on it for protection. Though Spanish moss is not parasitic in nature, it does "steal" water and nutrients that the tree would otherwise utilize. Spanish moss is gray-green in color and hangs in string-like fibers from the tree. Usually found on trees with diminished health, severe infestations can cause a greater loss of health, and the weight can lead to broken limbs, according to the Clemson University Extension. For control, remove moss by hand.