Slime flux, also known as bacterial slime or bacterial wetwood, is a bacterial disease of certain trees, primarily elm, cottonwood, poplar, boxelder, ash, aspen, fruitless mulberry and oak. A wound to the bark, caused by pruning, insects, poor branch angles or natural cracks and splits, causes sap to ooze from the wound. Bacteria may infect this sap causing it to darken and stain the bark, eventually taking on a foamy appearance and unpleasant odor. This slimy ooze becomes toxic to the bark and eats into the tree. The fermented sap attracts insects like flies, ants, and maggots.

Cause

Slime flux occurs when a wound is made in a tree trunk through things such as natural growth cracks, frost, insects, birds, lawn mowers, cat scratches, or pruning wounds, which causal bacteria can enter. Once inside the xylem, the internal pressure of the tree is raised, from the normal range of 5 to 10 psi up to 60 psi, due to bacteria fermenting and emitting a gas mixture of methane, nitrogen, carbon dioxide, and oxygen. This accumulation of liquid and gas causes that part of the tree to have a damp, dark brown appearance known as wetwood. Eventually, the pressure will cause the sap and gasses to burst through the xylem and out of cracks in the trunk and ooze down the side of the tree. This sap flux may be further infected by other pathogens once exposed to the air such as air-borne bacteria, yeast, and other fungi, at which point it is known as slime flux.

Causal agents

Causal bacteria for the initial wetwood varies depending on the species of tree. The bacteria are commonly found in water and soils. Enterobacter spp., Bacillus spp., Pseudomonas spp. Xanthomonas spp., Agrobacterium spp., Acinetobacter spp., Corynebacterium spp., Bacteroides spp., Clostridium spp., Edwardsiella spp., Klebsiella spp., Lactobacillus spp., Methanobacterium spp., Brevundimonas bullata, Paracoccus spp. and Luteimonas aestuarii have been isolated from wetwood in various tree species. Species of Prototheca have been isolated from slime fluxes.

Potentially affected plants