Extension Communications 3614 Administrative Services Building Ames, Iowa 50011-3614 (515) 294-9915

9/8/03

Contacts:
Barbara Ambruzs, Plant Pathology, (515) 294-1741, ambruzsb@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning Sept. 12

Slime Flux

By Barbara Ambruzs
Extension Plant Pathologist
Iowa State University Extension

Did you ever see a tree cry? You might think so if you've ever seen a wet, glistening stream seeping down the ridges of its bark.

Of course, this liquid really isn't tears. Instead it is a fluid produced by certain bacteria that inhabit many tree species. This disease is known as bacterial wetwood, or slime flux, and it is common in elm, maple, poplar and birch. Even after the slime dries, the bark stains a yellow to brownish color, indicating that at one time the tree was oozing.

Bacteria are microscopic organisms are made up of only one cell. Populations can increase extremely rapidly. Many bacteria have a slimy, protective coating. So, when millions of bacterial cells are in one pile they are usually oozy and gelatinous. The wetwood / slime flux bacteria often live deep within trees.

The wetwood/slime flux bacteria can tolerate low oxygen levels within the wood. Some bacteria even require an oxygen-free environment. Bacteria that can live without oxygen are known as anaerobic. The byproducts of their anaerobic lives are methane gas and liquids, resulting in a pressure build up inside the trees. These gasses and liquids usually have an unpleasant odor. Weak spots in the bark or branch crotches typically give way to the high pressure and allow the material to release. That's when the ooze begins to drip down the tree.

While inside the tree, the slime is usually clear, but it changes color to brown after it is exposed to the air. Organisms, including yeasts, other bacteria, fungi, and insects feed on the nutrient-rich broth.

The slime also contains chemicals that are toxic to plants. Therefore, dead grass or other plants can usually be found at the base of weeping trees. Slime poison also can injure the newest layer of live cells inside the tree.

Trees can defend themselves internally from a spreading infection, but wounds can create entryways for disease causing bacteria to start new infections in other parts of the tree. To gain entry, the bacteria require wounds, such as those from lawn mowers, animal chewing, digging in the root zone, or storm damage. Once inside however, bacteria symptoms can take several years to appear.

In elms, this disorder may cause wilting, leaf yellowing, and dieback that can resemble other infectious diseases such as Dutch elm disease, which is caused by a fungus. A laboratory test can confirm if the tree has Dutch elm disease.

Preventing wounds and stressful situations is the best way to reduce wetwood problems. However, there is no cure for bacterial wetwood / slime flux. Once a tree shows the symptoms of bacterial wetwood / slime flux, you can probably expect to see it again in following years.

Be sure to water plants when needed - especially during dry periods. Symptoms tend to be more severe when trees are stressed from drought. Check the soil moisture at about 10 - 12 inches down to be sure it is dry before watering and moist after watering. Avoid compacting the soil over the roots since compacted soil limits oxygen and water uptake.

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Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The fullsize photo is 408K. Caption: Slime Flux, also known as bacterial wetwood.

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