Dutch Elm Disease

Elms are beautiful and majestic trees that are certainly worth the disease prevention measures available against the devastation of Dutch Elm Disease (DED). Quick to wipe out Elms, DED is caused by a fungus that leaks toxins into the xylem (water-carrying vessels) of trees. Ultimately, water flow is so impeded that the trees wilt and die.

DED is spread not only by the elm bark beetle, but also from tree to tree through grafted root systems. So if you have elms next to each other and the disease has infected one, it may make sense to sever any grafted roots. Unfortunately, once the disease travels to the root system of a tree, its chances of survival are almost nil. If, however, the initial infection takes place in the crown, then treatment with a control and sanitation pruning to remove infested areas can be a viable treatment option.

Although we have disease resistant elms available to us now (Princeton, Liberty, Valley Forge, Olmstead are the most common available in the nursery trade), it will take a lifetime for these trees to reach the size and form of some mature elms. Dutch Elm Disease is very heavy this year and we have been injecting larger groves of elms through Central Park. We will also be beginning to treat elms throughout Riverside Park this week and for many residential and commercial clients.

Injection treatments are made by drilling at the base of the tree and pumping a control through the vascular system. Depending upon size and weather, one treatment can take up to 6 or 8 hours. Treatments are repeated once every 3 years, and the drilling site is small and heals relatively easily. I cannot stress enough that investment in this type of preventative treatment program is well worth avoiding the deterioration and removal of a beautiful tree.

To learn more about Dutch Elm Disease and available treatments, visit http://www.rainbowtreecare.com/diseases/dutch-elm.asp.

Take a look at some photos I took of trees suffering from DED the other day in this slideshow:



-Ken Almstead

Girdling Roots on a Bradford Pear

A girdling root is one that circles around the trunk of a tree rather than growing out away from it. The structural damage is twofold: Every root that grows around a tree’s trunk is one fewer root that offers the tree lateral support; additionally, as girdling roots grow, they press against the tree’s trunk, cutting into the tree like a self-imposed tourniquet.

For this Bradford Pear I photographed the other day, you can see that girdling roots eventually cut through the trunk so deeply that the structure was irrevocably damaged and the tree fell. This is the ultimate danger of unhealthy root systems.

Girdling roots are wholly a result of human involvement and only appear in the urban forest. Usually, a girdling root problem is established while a tree is being planted – and it gets progressively harder to correct from then on. In nurseries, trees begin their lives in small pots with little room for their roots to spread outward, so they begin to circle. By the time saplings are ready to plant, they often have many jumbled, circling roots. It is important to prune and rearrange these roots as part of the planting process, otherwise a girdling pattern is established. Girdling roots also appear when the natural growth pattern of a tree’s root flare is obstructed. Just like in the small nursery pots, if a tree root hits a barrier (such as a sidewalk curb) it will alter its course and potentially circle back around the tree trunk.

One more major cause of girdling roots is the absence of a root flare. The root flare is where a tree trunk transitions into its roots, and should be located just above ground level. However, trees are often planted inappropriately deep, burying their root flares in soil (or excessive volcano-shaped piles of mulch). Roots then have the opportunity to grow up around the buried base of the trunk, invisible to observers above ground.