Outdoor Services Crew

Thursday, June 30, 2011

Trunk Injection Treatments for Elm Scale on Campus

Some of the most impressive and interesting trees on our campus are the American and Augustine Elms.  We are lucky to have about 40 of these trees left on the main campus after the Dutch Elm Disease epidemic reached colorado in the 1980's, decimating elm populations along the Front Ranges' urban corridor.  We have not had any confirmed cases of Dutch Elm disease in the last decade but our Elm trees have suffered from other disorders and insect issues. 

One of the most damaging of the insect pests on our elms is the European Elm Scale, a very difficult pest to treat once it becomes established.  This insect is the armored scale present on the twigs and smaller branches of nearly any elm tree you might see in Boulder.  Many otherwise healthy and vigourous appearing elms have many small twigs denuded of their leaves due to the scale.  If unchecked, this dieback will move into increasingly larger diameter branches.  This scale insect is also the reason so many elm trees have massive amounts of "honeydew" misting off of them, sticking to everything under the tree.  This honeydew also feeds the production of the black sooty molds on the trunk and branches of the trees and on hardscapes around the tree.  Besides the nuisance factor, this insect is very hard on the trees' health, robbing the twigs and leaves of nutrients and opening the door to secondary decay organisms and weakening the tree substantially.
Over the past several years we have intermittently tried applying insecticides to our elm trees in an effort to slow down this insect.  This year, one of our vendors, Davey Tree Care, is utilizing a new system to administer the pesticide that we feel will do an excellent job of striking the pest while greatly reducing any chances of harming non target organisms, including people and pets, on our campus.  This system is called ArborJet and uses a pressurized cannister to push the insecticide into the cambium layer of the tree allowing the trees' own trans-evaporation processes to then move the product up the trunk and into the smaller branches and twigs where the scale is feeding.  This is a much more direct application of the product than a soil drench to the roots of the tree.  None of the product is disbursed into the surrounding environment and therefore cannot likely be contacted by non targeted or beneficial insects.  Only the insects that puncture the trees and feed are subject to the insecticide.  Most any insect feeding on the trees juices or foliage is not considered beneficial to the landscape.

Working within Integrated Pest Management practices means that in addition to using this pesticide, we will continue to practice other forms of plant health care for these trees, as well.  This will take the form of continued dead wood removal from the canopy, small amounts of structural pruning, and supplemental watering.  The sanitation of the dead wood is especially important in elms in order to lower the attraction of the bark beetles which can vector the Dutch Elm Disease.

The following photos show the insecticide being administered by a professional crew from Davey Tree Care Co. contracted to work on our campus.

Small holes are drilled into the outer layers of the tree and the injectors applied.

Then a pressurized cannister delivers the amount of material needed to treat the tree.  The amount of product needed is determined by the trees' Diameter at Breast Height.

We are hopeful that these trunk injections will help to turn the corner on contolling damage to our historic elm trees from this very resilient pest.