Question
We have a mature Fruitless Mulberry tree in our backyard and noticed a problem with it lately.  At the base of the trunk (right at the soil) a messy, putrid and wet soil has begun to emerge in the last two months.  I've dug up the soil to see what the cause is, and it seems to be coming from the roots of the tree!  I've looked all over the internet to see if anyone else has had this problem but I can't find anything.  The roots don't go near a sewer line which could have broken, which was my first guess.  The overall health of the tree seems fine.  Any suggestions as to what we're dealing with (is this a disease?) and what can be done to help?  Thanks in advance for your response.

Answer
Hi John,

What you describe sounds like Bacterial Wetwood disease. This is a common disease that affects the central core, bark, and roots of many shade and forest trees. Slime is the exudate generated from wetwood and is toxic to growing areas of the tree. Wetwood-infected tissue does not greatly alter the wood strength of most trees. Prevention of tree stress is the best management approach. The disease affects many species including mulberry.

The causal organisms (bacteria) include species of Enterobacter, Klebsiella and Pseudomonas, which are associated with wetwood. It has not been conclusively demonstrated that these bacteria cause the disease, but they are directly involved.

Symptoms:

Symptoms of this disorder may include a yellow-brown discoloration of the wood, generally confined to the central core of the tree. This affected wood is wetter than surrounding wood and is under high internal gas pressure. The gas pressure and high moisture content cause an oozing or bleeding of slime from wood, branch crotches, and roots. The ooze often is foul-smelling, slimy, and colonized by fungal organisms when exposed to air. When the slime dries, it leaves a light gray to white crust on the bark.  Wetwood slime is toxic to the cambium that produce new cells. It can prevent or retard callus formation when the tree has been wounded. Foliage, young shoots and grass die if slime flux drips on them. Wetwood also can be found just under the bark as dark streaks in the current season's wood or as a discoloration in several annual rings within the spring wood. This cambial or "surface" wetwood is common on drought-stressed trees. Root tissue also can exhibit wetwood symptoms as brown streaks extending from the diseased trunk into the center core and sometimes the outer wood of roots.

No effective methods exist to eliminate wetwood disease. Preventing damage and stress to a tree抯 roots and stem is the best way to avoid a serious wetwood problem. Drought conditions increase wetwood problems, so it is important that the tree receives adequate water, especially during spring and summer months.

Fertilizing wetwood-infected trees is recommended if the tree shows nutrient deficiencies. To help prevent disease spread within an infected tree, keep any injection holes shallow so they do not reach the inner wetwood core. If they do reach this core, the bacteria can spread outward.

Any tools that you have used in examining the root system should be treated at least 20 minutes in a 10% solution of household bleach to minimize the spread of the bacteria.

Under normal conditions, bacterial wetwood does not significantly affect the strength of the tree as the increased "pressure" from the slime inhibits fungal species that would cause the heartwood rot.  

Good Luck.