options for extensive canker on holly tree
This winter we learned we had some canker on our pear tree. I'm new to identifying canker, but hopefully we were able to remove it all. (Once the petals fall I'll give it another dose of Cu.) Meanwhile, on the other side of our yard, we've been wondering why our ~25' holly tree seems so sad. I brought some photos and a specimen to the local nursery, and--you guessed it--it's canker (I think bacterial). It's *a lot* of canker. I'd guess a third to half of this gnarled, heavily cross-branched tree is cankered. I started pruning it out, but eventually got overwhelmed: several hours looked like I hadn't even touched the tree. It's hard for me to imagine that I'll get it all, and meanwhile, even with oft-sterilized pruners, I suspect that I'm spreading the canker around more than I'm knocking it back. So my questions are these: Am I right to suspect that saving this tree is probably futile? Is it a terrible idea to lop off every branch and let it try to come back from the shock--look goofy-as-all-get-out for several years or perhaps forever, but at least not have given up? If I leave the tree in its heavily cankered state for a few months/years (I'm not in a position to remove the tree immediately), am I risking that the canker will spread to other trees in the yard? My (minimal) understanding is that cankers usually don't spread between species. But I'm not sure what all is packed into that "usually." What concerns should I have about this canker spreading? Anything else you'd recommend with respect to this situation? (Including better ideas for dealing with the pear canker; I'm particularly concerned because after pruning off so much, I only have maybe 50 bud clusters, with some major branches completely barren) If you decide to make my question public, please feel free to edit for brevity or otherwise.
Benton County Oregon
Hello. Cankers are caused by multiple pathogens not just bacteria. There are two things that will help your plants resist a canker infection; first avoid injuries to your plants and second keep your plants as healthy as possible as a healthy plant is more resistant to the disease. Lawn mower and weed eater injuries are preventable others caused by bad weather not so much. Be careful when pruning and when using any power tools around your trees, injuries to bark make it easier for the disease pathogen to penetrate exposed wood.
First the holly tree. Based on your description of the extensive damage to that tree, I think that once you are able to remove the holly tree, you should do so. Meanwhile be sure to destroy the residue from your pruning. Careful and frequent sanitation of your pruning tools is necessary to not spread the disease to other trees and shrubs.
Now for the pear tree issue. Again, avoid mechanical injury to the tree. Cut out existing cankers during the dry season making sure to cut below the visible canker tissue. Destroy infected tissues once removed. Sterilize tools frequently. Control weeds under the canopy of trees as they may be a source for the infection. Supplement the cultural controls mentioned above if necessary with chemical control with one application in October prior to rain and another application in early January. Carefully monitor tree for spread of canker. Again extensive damage to the tree may warrant its removal.
I have included a link from a publication from and OSU that discusses home orchard tree care, https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec631_0.pdf . This document gives you a lot of information on any fruit trees that you may have. If you have further questions I suggest that you call the Master Gardener information desk in the Benton County Extension Office and discuss the issues with them. The number is 541-766-6750.