Slime flux disease of trees

Several globe willow trees are growing in our mobile home community in Las Cruces. In the past few months, we have noticed that several of these trees have developed a disease, if that is the proper term. Sap flows from one of the branches and runs down the trunk of the tree to the ground. This sap is brown and at some times has a foamy look to it. Two of these trees have died and been removed. Recently, we noticed that other willows in the area have started developing this problem. We are worried because we have a fairly large willow in good condition. We are concerned that our tree will contract this disease. Is it contagious? What can we do to prevent this from happening?

Patience C.
Las Cruces

You are describing a common disease of some trees called �wet wood disease� or �slime flux�. This is a bacterial disease of the heartwood of trees. The bacteria that causes the problem is common in New Mexico and blows around in the wind. It often enters a plant through a wound caused by pruning or wind breakage of branches. It is contagious, but there is very little you can do to prevent it from infecting a susceptible tree. Willow, cottonwood, mulberry, and other trees commonly grown in New Mexico landscapes can be infected.�

The good news is that this is a weak disease that does not kill the tree itself. In fact, by altering the pH of the tree sap, it reduces attack by some more potentially lethal fungal diseases. It does weaken a tree to environmental stresses. Wet wood disease may have weakened the trees so that they more readily succumbed to the drought of the past few years. (Even though last summer was wetter than the previous years, the damage may have already been done.)

By properly irrigating the trees, you can help them survive. Willow trees have very shallow but extensive root systems that extend far beyond the edge of the canopy of the tree. When watering your tree, moisten the soil to a depth of 2-3 feet each time you water. Irrigation should be applied twice a month in the summer and once a month in the winter. Apply the water to the soil at the dripline of the tree (under the edge of the trees canopy) and outward for a distance of 10 or more feet (more as the tree grows). Do not apply the water to the base of the tree trunk. The roots at the very base of the tree serve as pipes to carry water collected by more distant roots to the trunk. These �pipe� roots do not absorb water, so water applied to them is not used effectively.

The globe willow is often a short-lived tree. As the trees succumb to disease and drought, you may consider replacing them with other types of trees.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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