Garden Clippings for January 19, 2019
Our Ash trees are gone. Swallowed up by the Emerald Ash Borer. Will our Oak trees be next?
Speculation is rampant on the issue. Officials from the Canadian Food and inspection Agency are on high alert. Some say Oak Wilt is already on the doorstep at Windsor and Sault Saint Marie, and it is only a matter of time before it enters Lambton County after which it will creep up through the rest of Ontario.
To better understand the threat of Oak Wilt let’s begin by not comparing Emerald Ash Borer to Oak Wilt. But unfortunately, that’s hard to do. The Emerald Ash Borer is fresh on our minds. It was late in 2002 that the Ash Borer was first detected in Ontario. The aggressive insect quickly attacked all types of Ash trees, boring its way into the tree and blocking the flow of water and nutrients. Within a few short years the first Ash trees died. Within a decade all or most of the Ash in Lambton County succumbed.
Today, every woodlot is littered with dead Ash trees. Some are still standing only because they have not yet fallen over. Drive down the 402 Highway and it is easy to spot the hundreds of fallen trees in the bush near Watford, Wyoming and Forest. What was once dense forest is now sparse.
We know for certain that Oak Wilt will not behave the same way.
Oak Wilt is a fungus. Oak Wilt is officially called Bretziella fagacearum. When Oak Wilt enters a tree, it behaves much the same way as a rotten potato, also a fungus. When one potato in the sac rots, the adjacent potatoes are next to go. Eventually the whole bag is spoiled. The potatoes that are spared are the ones that are have been separated from the lot.
The primary way Oak Wilt spreads from tree to tree is by root grafts. When Oaks are in a group or cluster, their roots can overlap and become entangled, eventually grafting so they share the same water, minerals and sugars. You and I can do nothing to prevent the spread of Oak Wilt fungus when their roots are connected. In the USA, where Oak Wilt has been busy for decades, attempts have been made to dig out huge trenches around packs of affected trees. These efforts are expensive, disruptive and do not come with a guarantee of success.
The second way Oak Wilt spreads is above ground via Oak Bark Beetles (Nutidulid beetles) unintentionally carrying fungal spores from infected trees to healthy trees. These insects are active in spring only and need an open wound or fresh entry point in order to poison a healthy tree.
You and I can do our part in the prevention of the spread of Oak Wilt by being careful not to cut, prune or damage Oak trees during the months of April to August when the Nutidulid Beetles are mobile. If during these critical months a wound is created by some mechanical method such as windstorm or other accident, the damage should be cut clean and sealed within minutes of cutting.
Next week’s Garden Clippings will take a closer look at the biology of Oak Wilt Fungus.