Ask Mr. Smarty Plants

Basic elements that influence tree health include sufficient oxygen in the soil, water and light and a proper balance of nutrients. Too much or too little of any of these environmental conditions may cause plant stress. Urban trees often have paving over some of their roots, and can also be affected by pollution. These and other environmental conditions may weaken the tree and makes them more susceptible to insect and disease attacks.  The elm is not generally a long-lived tree, probably because of the problems to which it is susceptible, but 12 years is not very long in tree life.

Of course, the first thing that comes to mind when an elm tree is in trouble is Dutch Elm Disease, which is an almost-always fatal disease of elms. You did not say which elm you had. In Texas, the native elms are Ulmus americana (American elm), which is highly susceptible to the disease, as well as Ulmus alata (winged elm), Ulmus crassifolia (cedar elm), and Ulmus rubra (slippery elm), all of which range from susceptible to somewhat resistant. This site from National Forestry Services Identify and Manage Dutch Elm Disease will give you extensive information on symptoms, prevention and treatment of the disease.

However, the symptoms as you have described them sound more like a canker disease. The information and pictures in this site from Kansas State University Extension Plant Pathology Canker Disease in Elm Trees is more specific. As a rule, Ulmus americana (American elm) and Ulmus rubra (slippery elm) are not severely damaged by cankers. To try to avoid cankers developing, avoid bark injury, such as being bumped by machinery or mowers and edgers. Prune out branches exhibiting cankers and remove them. Some more pictures of cankers.

It is difficult to diagnose or recommend treatment from a distance. We suggest you contact the Texas A&M Agrilife Extension Office in either Tarrant or Denton counties. Both linked websites have contact information, and they would be in a better position to know about disease or pests of the elm trees in your area. It would probably also be advisable to have a licensed arborist look at the tree and see if any treatment is feasible.

Ulmus alata

Ulmus alata

Ulmus americana

Ulmus americana

Ulmus crassifolia

Ulmus crassifolia

Ulmus rubra

Ulmus rubra