Travelling around southern Ontario, it won’t take long before you come across an individual tree or stand of trees that are stone dead, despite being perfectly healthy as little as 2 years prior. Trees that go from perfectly healthy to standing dead in a short period of time are generally either terminally diseased or infested with a deadly pest. In this part of the country there are several pests and diseases whose cycles ebb and flow over the course of years and decades. There are some, however, that leave a lasting impression where they settle and mar the skyline with the crispy tips of their victims among the adjacent, soft swaying canopies.

 Effects of Dutch Elm Disease*                                                        Emerald Ash Borer

Emerald Ash Borer and Dutch Elm Disease are an insect and a fungus that have devastated our Ash and Elm tree populations in the past. These pests and diseases were so thorough in their destruction that it is rare to find any left standing, where they were once so prevalent in this city. The ones that did survive were likely injected during the early stages of the invasion with a product called TreeAzin for Emerald Ash Borer and Arbotect for Dutch Elm Disease.

Both these products work by drilling through the bark of the tree and “injecting” the product directly into the vascular system of the tree. It is then carried up into the canopy using the tree’s systems for distributing water and nutrients. TreeAzin works by killing the larva inside the tree and sterilizes the female beetles who eat the leaves, while Arbotect kills the fungus that blocks the Elm’s ability to transport nutrients between the roots and the canopy. The trees that survived will need to be injected every 1-3 years until there are no more cases of the pest or disease in the area, which could take years if not decades.

Trees being injected

More recently, Cohen and Master and other industry professionals have been using TreeAzin to fight the spread of Gypsy Moth and save large trees that are otherwise untreatable. The treatment process is the same, where small holes are drilled through the bark and the systemic pesticide is carried into the leaves. The caterpillars hatch and start feeding in the spring (mid-May to early June), they ingest the pesticide, stop feeding, and die shortly afterwards. If Gypsy Moth defoliate a tree for more than 2 consecutive seasons, the tree will likely be terminally damaged.

While the best option for treating pests and diseases is preemptively maintaining good tree and soil health, there are certain pests and diseases that are intent on destroying their hosts regardless of the tree’s condition. Injections are a valuable weapon in an arborists arsenal to fight the onslaught of a tree’s never-ending and relentless enemies.

By: Rachael Kowaleski, BES
Consulting Arborist, Cohen & Master Tree and Shrub Services

*Photo credit for Dutch Elm Disease photo: