Have You Seen This? Or This? (Growths on Beech & Weeping Cankers on Pine)

March-April 2012

I was walking in a beautiful maple-beech forest just east of St. Thomas with some friends before Christmas and we noticed some unusual growths on the American beech trees. A closer look revealed black, dense, almost woolly looking tissue on small twigs and also on the main stem and some persisting leaves. It was about -18C with the wind chill and we did well to stop long enough to take a few photos and collect a small sample. 

Looking under the microscope back at my office, I could see that the wooliness was made up of masses of bead-like growths. This is a classic characteristic of Eriophyid mites and my best guess at the causal organism. According to the literature, it is estimated that hundreds of species of eriophyid mites are out there feeding on all kinds of woody plants, but many of them have not yet been described. Eriophyid mites are said to be very host specific but I was unable to determine what species of mite that was causing this type of gall on the beech. I’ve looked through all my books and on the internet to see if I can find a description or photo that matches the symptoms on those trees with no luck to date.

On another walk through the Arboretum at the University of Guelph, I noticed a number of white pine with chlorotic foliage. Now chlorotic foliage isn’t unusual in Guelph, our soils are high in calcium and magnesium and their chemistry often locks up micronutrients (e.g. manganese, iron) in a form that is unavailable to plants. A closer look revealed weeping cankers on the main stem and on some of the larger branches. The chlorosis and dieback seemed quite patchy in the canopy, sometimes just on one side. 

I’ve received a lot of inquiries about dieback on white pine in the last little while and many of them seem to match the symptoms I’ve described here. When I cut into the weeping bark, I found that large expanses of the cambium tissue are indeed dead and have turned a rusty-brown colour. Most of the symptomatic trees I have seen were planted at least a decade ago, many with a DBH of 10 inches or greater. Yet they are succumbing to a canker/wilt problem all of a sudden? 

Some of the literature is suggesting Cytospora or Botryosphaeria as potential pathogens. More investigation, destructive sampling and lab analysis will be required to try to identify the causal agent behind this decline of white pine in the landscape. If you are removing symptomatic branches from these trees, make sure you are disinfecting your pruning tools between each branch removal to prevent spreading the disease further.   

Getting back to my nature walks, one of the skills I’ve honed over the years is birding by ear. I can identify more bird species by their call or song than I can by their sight and that skill earned me the nickname “bird girl” when I was younger. Yes, there were other nicknames too but we won’t go there. 

It can be a little distracting some times when I’m working outdoors and people can often tell if I’m not fully listening. Usually my bird call identification insights are met with a pause and a polite smile. But some day this skill is going to come in handy, I just know it is. In the meantime, I’ve turned the tables on you in this column. If you can assist me with the white pine issue, please give me a call or email.  

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