Cottage Q&A: Yew tree disease

In the last few years, we’ve noticed that the yews on our property appear to be dying. This is not just happening on our lot, but all around the lake. We were wondering if you knew what is causing this.—Davis Zvejnieks, Otter Lake, Ont.

We can’t give you a definite answer. “It’s impossible to diagnose what may be affecting the yews without samples of the trees,” says Sylvia Greifenhagen, a forest health researcher with the MNRF. But there are a few possibilities.

Possibility No. 1: Wet feet. Remember last year, when almost all of cottage country flooded? “Yews don’t like to get their feet wet for prolonged periods,” says Greifenhagen. “Canada yew thrives in moist soil, but in very wet soil conditions, the roots will begin to die, and the needles will turn yellow and brown.” Inspect the needles. If wet conditions are the problem, you’ll also see brown bumps (called “edema”) on the undersides.

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Possibility No. 2: A fungal infection. Certain fungi can cause needle blight in yew; look for black fruiting bodies on the needles. On the other hand, if you’ve noticed light brown mushrooms growing at the base of the dying yews, Armillaria fungi could be the culprit. The fungus gets into the yew’s roots and can eventually girdle the tree. There’s not much you can do to rehab a tree with root damage, but you can help trees with needle blight by pruning away the affected needles.

Possibility No. 3 (and this is the most likely): A combination of factors. “Environmental conditions greatly influence the severity of leaf and needle diseases,” says Greifenhagen. “In general, a drier spring and summer will result in fewer foliage diseases than a wet, humid spring and summer.” 

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Don’t worry. Yews are more resistant to disease than other trees, and they can survive losing some of their needles. So, if a drier summer is on the horizon, there may just be hope for them yet. Yews can do it!

This article was originally published in the June/July 2020 issue of Cottage Life magazine.

Do you have a question for Cottage Q&A? Send it to answers@cottagelife.com.

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