The Mimosa - The Beauty and The Beast

I usually get a lot of questions this time of year to help identify a specific blooming tree. Some of you may already know what I'm talking about, a rather feathery leafed specimen similar to the honey locust tree that is covered with beautiful pom-pom pink to peach colored blooms. It's mostly ladies that love the look of this tree, and want one in their landscapes. Hopefully, this e-mail will not only serve to help identify the tree, but keep you from making the mistake of planting one. Yikes ... did he just say DON'T plant one? Yep, I don't want you to plant one.

This beautiful, blooming specimen is called the Mimosa tree. While it looks beautiful now, the rest of the year it's either pathetic looking or overwhelmed with insects and disease. In Hawaii, the Mimosa is a weed. In Texas, it's susceptible to borer insects, which can girdle the cambian layer just inside the bark and kill the tree. Yet, its susceptibility to the Mimosa web worm is the real reason to avoid a Mimosa. The Mimosa webworm is highly destructive to honey locust trees. It is the larval stage that feeds on foliage and causes the damage. When fully grown, larvae are about a half-inch long (12-16mm) and are gray-brown or sometimes pinkish in color with five narrow white longitudinal stripes. They spin webs around flowers and leaves, and feed on the foliage within the protection of the web. The surface of webbed leaves is skeletonized, causing the leaves to turn brown and die.

Then there's Mimosa wilt, the fungal disease. The classic symptoms are wilting and yellowing of the foliage. In some cases, the leaves will become dry and shriveled while remaining green or yellowish for some time. Later, the leaves fall, and the branch dies. Usually the tree is affected branch-by-branch, and dies completely within a year of the onset of symptoms.

Another common characteristic of the disease is brown discoloration in the sapwood, especially the outermost annual ring, caused by gum-filled tissue cells. This hinders or completely inhibits water movement from the roots to the aerial portion of the tree. This discoloration can be found in trunks and branches even before the leaves wilt. During the summer months it is not uncommon for the bark of infected trees to rupture and exude fermented, frothy sap. Many insects are readily attracted to this sap. The fungus lives in the soil and enters the tree through the roots. Dead and dying trees should be cut down and destroyed to avoid the spread of the disease.

So, do you still want to plant one?

If you already have a Mimosa, you can treat for insects with chemicals like Malathion or systemics like Bayer products or anything with Imidicloprid. But, if you get the wilt, there are no known chemical controls.