The live oak is a southern tree and grows best in the warm climates along the Gulf of Mexico in the deep south. In these areas the tree behaves stays green through the winter months, and loses leaves in the spring which are quickly replaced by new ones. Live oaks grow along the Atlantic Coast as far north as Virginia and in these areas, the tree is semi-deciduous. The tree loses its leaves in the spring and sometimes in the fall depending upon the weather.
Lack of Moisture
To determine if the lack of moisture is a causing leave to turn brown, dig a small hole 12- to 18-inches deep two or three places underneath the tree. Examine the soil to determine if it is dry, moist or muddy. If the soil is dry, use a soaker hose or any apparatus that emits water slowly to wet the ground completely around the base of the tree to a distance of about three feet beyond the drip line. The drip line is the outer edge of the foliage where rain water ceases to drip.
Water the tree slowly enough to soak the ground to a depth of 12 to 18 inches. The tree should watered in this fashion once a week until you receive rain.
Too Much Moisture
Live oak trees do not do well in poorly drained areas. If the ground beneath your live oak remains muddy or water-soaked for periods of several days, water the tree less frequently or provide better drainage. Drainage systems can be as simple as open ditches that drain water away from the roots of tree.
If the tree is in a lawn or public area, an underground drainage system may be more appropriate. To install an underground system, find the lowest point beneath the tree and install a water collection basin in the ground and cover the top with a grate. Run flexible perforated drainage pipe from the basin to an existing ditch or other feature that carries water. If there is not an existing place to catch the drainage, then dig a hole at the end of the pipe about three feet wide and about three feet long and then fill the hole with gravel. Install the drainage pipe with the small holes on the bottom so that water can drain along its course.The remainder of the water will percolate upward through the bed of gravel and evaporate. The drainage pipe needs to be long enough to take water away from the tree.
When buildings are constructed near live oaks, dirt from the basement or foundation is often spread over the tree roots. This action inhibits oxygen supply to the roots, causes leaves to dry and fall from the tree, and, after a period of a few years, may cause the tree itself to die. Often contractors try to protect plants with tree wells but they never seem to make them big enough. A tree well should extend just beyond the drip line.
If this condition exists, either enlarge the tree well or regrade the area around the tree to the original ground level.
Mistletoe, a fleshy leathery plant, is a parasite that gets its food from a host tree. If mistletoe is abundant on the limbs of your tree, remove it if possible. An abundance of mistletoe will weaken the tree and cause its leaves to dry. Unfortunately mistletoe eventually grows back after removal so controlling it is a never-ending job. Removal of branches that contain a large number of the pests should also be considered.
If you live in an area where oak wilt occurs, then this could be a reason for the dry leaves.Oak wilt usually does not affect just one tree. The infection moves overland in a wide band and is spread through connecting tree roots and sap beetles. Leaves on an infected tree wilt and the leaf veins usually turn yellow. Affected leaves fall from the tree and the foliage gradually thins until the tree dies.
Contact a tree company or a county agricultural extension agent if you suspect oak wilt.