In oaks as with people, bleeding is a sign of a serious problem. Oak trees may not have blood, but they can exude liquids that look reddish or dark colored. The liquid oozes out of cankers or cracks in the bark. It is often a sign of a serious condition called sudden oak death, but may also be a symptom of some less severe problems.
Sudden Oak Death
Sudden oak death is caused by the fungus Phytophthora ramorum. It can infect red or intermediate oaks like coast live oaks (Quercus agrifolia), California black oaks (Quercus kelloggii) and canyon live oaks (Quercus chrysolepis). It does not appear to affect white oaks. The most obvious symptom is bleeding cankers on the trunk usually about 3 to 6 feet of the ground. Cankers usually appear on intact bark without any obvious holes or wounds. The bleeding is usually reddish, sticky and spotty. Leaves may rapidly turn brown within a month without any signs of illness or decline, hence the name sudden oak death. The disease has only been seen on the West Coast in California, Oregon and Washington.
Three other Phytophthora species can also cause bleeding oaks: P. cinnamomi, P. ramorum, P. quercina and P. kernoviae. These fungi produce cankers that bleed a reddish-brown to black, gumlike liquid from lesions. The inner bark may have pink or brown staining and a defined margin on the cambium. The only way to determine if it is Phytophthora ramorum or another species of Phytophthora is to submit samples for analysis. Contact your local agricultural or county extension for information on how to have an oak tree tested.
Wetwood is a bacterial infection that causes bleeding symptoms similar to sudden oak death. Wetwood can affect any type of oaks including white oaks. Bleeding is abundant, watery, foul smelling and will occur on the trunks and limbs. Foliage on the upper crown may wilt and branches may die back, but otherwise the oak will have no other symptoms. Wetwood usually occurs after a wound.
Armillaria root disease can cause a resinous, gummy or liquid substance to appear on the lower trunk that can be mistaken for bleeding symptoms of sudden oak death. It usually causes a general decline where the foliage wilts, fades and becomes discolored and sparse. Thin white fungal material, known as mycelial fan, will also be found growing between the bark and wood on infected trees. Bleeding and mycelial fans are more common on conifers than on oak trees.