There are about 600 species of oak found in the world. Two common genera of oak trees are Lithocarpus and Quercus. The leaves of these trees are characterized by lobed margins and spiral arrangements. Few species however, have smooth or serrated margins. Flowers of oaks are in the form of catkins and their production takes place in spring. A cup-like structure known as cupule bears the nut of oak. This nut fruit is known as acorn. The live oak tree is susceptible to a few diseases. Some of these diseases cannot be controlled at all, whereas others can be treated with proper preventive measures.
Oak Root and Butt Rot: The causal organisms of root rot in oak tree are fungi, parasitic algae, and water molds. Excess irrigation results into the growth of these organisms in the root zone of oak. Common pathogens responsible for the cause of root rot in oaks trees are Phytophthora spp and Armillaria mellea. These pathogens prefer a moist environment for their growth. One of the commonly observed symptoms of root and butt rot is that the tree may get blown down during winds. Dying limbs and sparse foliage are also observed.
Mistletoe: The parasite called mistletoe feeds on oak trees and furthers weakens them, if not controlled in a timely manner. Dissemination of the mistletoe takes place by means of birds. Removing the mistletoe parasite from these trees can be a temporary solution. However, for long term/permanent control of this problem, the damaged parts need to be removed completely.
Oak Wilt: The wilting of oak tree results from infection of fungus. The fungus attacks vascular system of the oak tree. Water and nutrient supply required for growth of this plant is blocked. Discoloration of the leaves of oak tree is the first observed symptom. The leaves start to turning yellow and wilt as the disease progresses. In about six months from the time of infection, the tree dies off. There is no way that oak wilt can be controlled. Burning branches and disposing off the wood is the only means to get rid of wilt.
Drippy Nut Disease: Acorn weevil and wasps are carriers of the organism which causes drippy nut disease in oak trees. Erwinia quercina, the bacteria is responsible for this disease. The above mentioned carrier insects puncture the acorns on the trees and transfer bacteria. Symptoms of the drippy nut disease are low acorn production and dying of branches. The disease is not curable. However, it should not be a cause of concern as the disease is not much of a threat to the plant.
Sudden Oak Death Disease: A full-grown and mature oak tree is more prone to this disease than the younger ones. A waterborne fungus called Phytophora ramorum is the causal organism of sudden oak death disease. Dissemination of this fungus takes place in the form of spores. Modes of dissemination include the irrigation water, gravel, contaminated soil, and wind-blown rain. Signs of this disease can be observed in the form of bleeding canker found on tree barks. Phosphate compound and fungicides are used as preventive measures. If the disease reaches its advanced stages, the damage becomes irreversible.