I have just, after some hours on the internet, realized that some of the pines I am growing have been infected with Pine Pitch Canker, which is a fungus infection that affects Knobcone, Monterey and Bishop pines as well as many other native California species.

The infection, which seems to be affecting about half my seedlings, is concentrated right at the root base, where I cut the taproots off when they were six weeks old. When I dig down a little into the soil and look around the trunk and nebari for signs of oozing sap I see that there are places where the soil granules are all glued together by sap. I also have one tree that I had started as exposed root style; there is sap oozing out from around the area where the old cut was down the exposed roots toward the soil.

I initially thought these problems were being caused by an insect infestation, but this is much worse; there is no known treatment for this fungus. I have written to a couple plant pathologists at UC Davis requesting an opinion but so far not received a reply. The infection, according to web sources, is localized inside the plant and will not spread to other parts of the tree internally, however it can be spread by insect activity (ants!) and obviously via bonsai tools that are not sterilized. Here is the website where I found most of the information:

http://frap.cdf.ca.gov/pitch_canker/

I haven’t decided whether or not I will simply discard the infected plants as I have invested a considerable amount of time and energy already in their care. According to the site some trees will recover from the infestation…but I can’t decide if it is worth the risk to other trees in my yard. What’s keeping me from just chucking them is that the fungus is obviously prevalent in San Francisco because I have seen sapling Monterey Pines dying for no good reason on Bernal hill, and I believe the full size one in my yard has a small infection spot. Still, not infecting my older Monterey Pine is a top priority and I hope that I am not already too late.

The lesson to be learned from this for me is that, at the very least, you must sterilize your tools when working with trees known to be susceptible to diseases. The older Monterey Pine bonsai in my yard had one branch die for no good reason last year, and now I know it may have been this fungus. I cut candles on the tree this year, and while I believe that I sterilized my scissors prior to doing so I can’t be certain. Furthermore, since there is more than one source for the fungus in my yard it wouldn’t surprise me to find more branches dying on that tree in the next couple years, the infection having entered after I cut the candles on it this summer. The whole thing makes me almost just want to stop growing Monterey and Knobcone pines…but not quite. So far I’ve lost almost one out of four of the seedlings that I had two years ago when I cut the taproots, but who knows, maybe one or two of them will prove resistant to the fungus and I’ll have a nice bonsai, if not, it will have been a hard lesson.

Tags: pests, Pines