Sunday, October 14, 2012

Ashes before the invasion

A White Ash (the yellow tree)

I went to a meeting about the Emerald Ash Borer (pdf) last week. It seems like this is the year that this nasty bug went from being a small infestation to a general epidemic for the Ottawa area. It was first found in eastern Ottawa in 2008. There have been predictions that it will wipe out all the ashes but for a few years if you weren't in the affected areas it didn't seem to be spreading very quickly. Now, this fall, the report is that it has spread to all parts of the city including the rural areas. The prediction now is that if you want to save your ash trees you should start giving them the expensive TreeAzin biannual injections next year.

So far the Manordale-CraigHenry area has been lucky but according to this map the first cases have been found in this neighbourhood. Ashes weren't planted along Hunt Club Road in the 2009 to 2011 tree plantings as we knew the ash borers were coming but ashes make up a significant portion of the trees planted in 1995. I went out the other day to inspect a few of the ashes to see if I could find any of those D shaped holes that the adult Emerald Ash Borers bore out in order to escape from the tree. I didn't find any holes but I didn't really expect to as I don't think they have reached here in significant numbers yet. I'll keep a look out next summer for the adults.

The ash trees in the 1995 planting area are about 6inches in diameter and are just starting to get their distinctive deeply furrowed bark. They aren't the largest most vigorous trees and tend to be out-competed for sunlight by the silver maples and the poplars. Some of them have died off already. I inspected under the bark of one of the dead ones but I didn't find any tracks indicating it was a victim of the ash borer. In the above photo you can see the yellow ash tree only gets enough light because it is at the edge of the wood, otherwise, it would be thoroughly dominated by the still green maple tree. I'm not sure that competition is the entire story though, one ash tree in a good open location along the forest edge died two years ago for no apparent reason. That is the one I searched without success for evidence under the bark of the ash borer.

Although the ash trees in the 1995 area are likely goners due to the emerald ash borer's eventual arrival, they have already cast their seeds and there are a multitude of seedlings growing up on the north side of the berm. I am more hopeful of their survival. First, they will hopefully be still too small when the height of the infestation hits the area. Second, I hope the parasitoid wasps will come in time to save the day for these small seedlings. US scientists have introduced three different types of wasps that are the natural predators of the emerald ash borer and that are able to naturally control their population in northern Asia. One of the panelists at last week's meeting said he hoped to see some balance brought back to the EAB population in five to ten years time. That would be too late for today's trees but it gives hope that today's seedlings might still have a chance.

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