What Causes Foam to Come Out of an Oak Tree?

Wetwood

• When foam comes out of an oak tree, the specimen may be suffering from bacterial wetwood, a disease also known as bacterial slime, slime flux or alcohol flux. Several species of bacteria attack the inner wood of the tree, first showing their presence as a yellow or brown discoloration of the bark that typically focuses around the center of the tree. A high internal pressure and gas develop as a result of the bacterial decay of the wood.

Foam

• The pressure forces a slimy fluid to seep from the tree via cracks in the bark. The slimy ooze emits a foul odor similar to stale alcohol -- a trait that lends itself to one of the disease's common names: alcohol flux. It is quickly colonized by yeast when the slime is exposed to the air. Upon drying, the slime leaves behind a white foam or crust on the bark of an oak tree.

Transmission

• The foam will exist anywhere on an oak tree where the bacteria is present. When the foam or ooze drops on branches or leaves, the bacteria spreads to those areas. Upon falling to the ground, the foamy bacteria will kill grass beneath the tree. Wetwood bacteria exist in soil and water and enter the tree through wounds to the root system. It is also possible for the disease to develop in seedlings that came from infected seeds or diseased parental cuttings.

Management

• There are no chemical control measures available to eradicate wetwood disease. Maintaining the health of the tree and minimizing wounds and cuts to the wood and root system will help to reduce the likelihood on an oak being attacked. A tree infected with wetwood should receive regular fertilization to help it combat nutrient deficiencies. Gardeners may notice an influx of insects to the tree, specifically flies and sap beetles that feast on the slime, but these insects do no additional damage and do not demand control.