Bacterial Wetwood & Slime Flux
SYMPTOMS: Profuse sap flows (fluxing) from trunk wounds and/or pruning cuts causes a vertical light or dark streak of residue on the bark. Leaves in the upper crown wilt and drop prematurely, and branches may die back. The flowing sap has a foul odor and may actually form bubbles as it flows out of the tree. The sap may be toxic to under story vegetations such as ground covers.
Many species are susceptible to wetwood infection:
Apple Hemlock Mulberry Redbud
Birch Hickory Oak Sycamore
Elm Linden Pine Willow
Fir Maple Poplar
CA USE: As implied by the name, wetwood infection is caused by bacteria entering a tree through wounds in the bark. Wetwood may not develop until a few years after the initial infection, since the bacteria require low oxygen levels to survive and can inhabit the inner layers of sapwood and outer heartwood.
The bacterial growth causes fermentation of the sap. Gases are produced (primarily methane) which can build up under high pressure. It is this pressure, from 5-60 p.s.i., that forces the sap to flow from wounds or cracks in the bark.
Fluxing occurs from spring to fall and primarily in the summer months when the bacteria are most active. In milder climates fluxing can occur year-round. The exuded sap is often colonized by additional bacteria and fungi, producing a slimy brown mass. This material is appropriately called slime flux.
The unpleasant smelling slime flux is more alkaline than sap from healthy wood. It is toxic enough to retard or even stop callus formation on the lower edge of wounds. Without the complete development of callus tissue, the tree is unable to close the wound. Leaves, twigs, and grass can be killed by the affected sap, and bark eventually bleaches to a whitish-gray color where it was contacted by the slime flux.
SOLUTION: There are currently no anti-bacterial product treatments that will eliminate bacterial wetwood. The infection is chronic and the bacteria can remain active indefinitely. Removal of infected branches will not cure the problem because the bacteria are usually not localized, but rather are widespread throughout the tree. Removal of dead or decayed branches is always recommended and will contribute to the overall health of the tree.
Sap fluxing can be reduced or stopped by the installation of a drain tube. This slanted tube relieves the pressure caused by the internal fermentation and allows the infected sap to flow out and away from the tree.
When used in combination with a drain tube, fertilization will help stimulate growth and the tree may be able to "outgrow" the infection.