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8:59 PM Thu, Feb. 21st

Column: Is your willow oozing?

KINGMAN - There are more than 350 different varieties of deciduous trees and shrubs in the Willow (Salix) family.

The Willow family is relatively a fast growing, weak-wooded, short-lived species. They are usually planted where there is an abundance of water. All have shallow invasive roots and are hard to garden under. Most are subject to pests/diseases: tent caterpillars; aphids; borers; spider mites; in desert areas, Texas Root rot; as well as slime flux and Frothy flux disease.

Slime flux

Globe willows are one of the several fast growing trees that are subject to slime flux, a bacterial disease of trees which is also known as Bacterial Wetwood disease. The most noticeable symptom of bacterial wetwood is liquid weeping from openings in the tree bark. This liquid ooze is known as slime flux. Bacterial fermentation of the sap during warm weather produces gases, causing pressure in the affected wood. The pressure forces flux out of the tree by the path of least resistance: cracks, wounds or branch crotches.

The liquid flux at first is colorless, later turning tan and darker. Once exposed to the air, the flux will become contaminated with other bacteria, yeast and fungi resulting in a foul-smelling, slimy, foamy substance.

If slime flux runs down the tree for an extended period of time, it may cause the bark to decay and eventually may damage the cambium. The cambium is the regenerative layer of tissue between the bark and the wood that is responsible for the tree's diameter growth. The cambium produces new wood and bark each year and is directly related to tree vigor.

Fluxing of sap may also cause toxicity in the sap that is carried to branches, thus resulting in wilting and defoliation of leaves. Plants adjacent to the tree trunk may also be killed or damaged by toxic sap exuded from wetwood wounds.

Slime flux alone rarely causes tree death but may lead to secondary pathogens (microorganism such as a bacterium that causes disease) that combine for continued tree decline and eventually death.

Wood-infesting and other insects are attracted to the flux exudates. These insects are likely to invade the tree as well as lay eggs and reproduce in the fluxing material.

There is no control for slime flux. Preventing damage and stress to the tree, its roots and its stems are probably the best way to avoid a wetwood problem. Drought conditions tend to increase wetwood problems, so it is important that the tree receive adequate water during the growing season.

Alcoholic flux

Frothy Flux is not related to Bacterial Wetwood (Slime Flux) even though they both have some of the same characteristics.

Frothy flux invades young trees as well as well established trees, killing the cambium and contributing to the tree's death often within a few years.

The organism - not yet positively identified - will invade the tree through freeze damage, pruning wounds, by insects or mechanical injury caused by lawn mowers, weed whips or other devices.

Once gaining entry to the cambium layer, fermentation of the bark cambium and inner sapwood layers of the tree occurs. This results in a froth that exudes through cracks in the branches and trunk of the tree at the site of attack. The frothy alcoholic flux is acidic, nearly colorless, and often gives off a fermentative odor (similar to stale beer).

Frothy flux often invades the tree in a branch crotch that has cracked or split. The growth habit of the globe willow is such that these branch attachments are naturally weak and prone to splitting in high winds.

In some instances, frothy flux invades larger branches and trunks, maintaining itself under the bark and does not cause the typical frothing ooze. The first symptom of infection for these older trees is not foam but the yellowing of the leaves and dieback of the branches immediately above the affected site.

When tapped with a blunt instrument, one often hears a hollow sound in the affected area. When digging into the area with a heavy knife, one finds the ooze typical of frothy flux just under the bark, often encompassing large areas of the cambium and sapwood.

Larger, reasonably healthy trees seem to outgrow the problem. A weaker tree may have frothy flux for a year or two; the problem may seem to go away for a year or two and then reappears. Improving the health and vigor of the tree helps reduce the chances of the problem becoming severe.

The common recommendation for eliminating or helping solve the frothy flux problem on globe willows is to remove all damaged, decaying tissue down to the wood as far back as necessary to eliminate any brown or yellowish streaking of the cambium or sapwood. This area is then swabbed with alcohol and a coating of amber shellac put on the wound in hopes of retarding any further infection. This treatment is only advised when the disease is in a small area of the tree.

For more information, contact The University of Arizona Mohave County Cooperative Extension at 101 E. Beale Street, Suite A, Kingman.