Palo Verde Foaming

Q. I have two Palo Verde trees in front of my house. One seems to be fine while the other has struggled for four years. I am told the tree is healthy but every summer it leaks white, sticky foam from the trunk. This foam attracts bees and beetles. The tree has received professional borer treatments twice a year but it’s still bad.

Foam coming from trees that attract flies and other insects are a good sign of slime flux or wetwood disease.

A. Save your money. This is not an insect problem. It is a disease problem but a disease that will not kill the tree. Let me explain.

            You mentioned bees and beetles are attracted to this foam. I am 99% sure, based on the picture you sent and your description, this is a disease called slime flux, sometimes called bacterial wetwood. It is a nonlethal disease to the tree. It attacks only dead or dying wood inside the core of the tree.

            Nonliving wood inside the tree cannot fight off disease microorganisms because it is dead. The only microorganisms which feed on this wood are "saprophytes". Similar microorganisms feed in compost piles and convert raw waste into compost.

            These microorganisms do not feed on living parts of the tree because living parts of healthy trees can “fight back”. Bacteria involved with slime flux create a foam with a characteristic smell of fermenting yeast or brewing beer. This "yeasty" smell attracts flies, bees and other insects such as beetles because this smell resembles rotting or fermenting fruit.

            Normally, this disease bothers us because of these insects and its general “ugliness”. It does not hurt the tree. It may bother us because the foam dripping down the trunk of the tree causes discoloration of the trunk and unsightliness.

            Probably this infection was transferred to this tree by unsanitary pruning practices. I always emphasize sanitizing and sharpening pruning equipment. When a tree is infected with a disease, it is extremely important to sanitize the pruning equipment before pruning a new tree.            There is no cure for this problem. You and the tree must live with it.

            Some arborists may drill a hole into the tree trunk and insert a metal tube just below the foam and sticks out of the trunk. This foam drains inside the tube and drips to the ground without touching the trunk. Make sure any tools and equipment which touches the inside of the tree has been sanitized thoroughly.