Things That Go Crunch In The Bark

Photo by Gevork Arakelian

By Frank Landis, Chairperson Conservation Committee

There's something about reading about Polyphagous Shot Hole Borers and commenting on the North County Multiple Species Conservation Program (MSCP) that just inspire me.  Sadly, I'm not sure anyone will appreciate what I'm thinking about.

Probably most of you are aware of the Shot Hole Borers (http://ucanr.edu/sites/pshb/ is the easiest source of information).  There are two species that are physically indistinguishable, but which are genetically distinct and come from different parts of Asia.  In San Diego County, we have the Kuroshio Shot Hole Borer (Euwallacea sp. I'm still looking for the specific epithet.  Let's call it KSHB), and it also has been found in Orange County and Santa Barbara as well.  Up in LA and Ventura, they have the Polyphagous Shot Hole Borer (also Euwallacea sp.  I'm still looking for the specific epithet, and I don't think it has one either. We'll dub it PSHB). 

The problem with these two non-native beetle species is that they like to burrow into the trunks of trees, and like other ambrosia beetles, these tiny pests –they're about the size of a comma or a period on paper—bring their own species of fungi with them (Fusarium euwallaceae and a Graphium species).  These fungi, along with the beetle galleries in the trunk, kill the trees. 

The bad news is that these beetles aren't all that specific.  Both of them love willows, alders, sycamores, and cottonwoods (and castor beans and avocados), but the PSHB has more hosts (49 species to date) than the KSHB (15 host species known so far.  You can read about the hosts at http://ucanr.edu/sites/pshb/overview/Hosts/ ).  The worse news is that they're rather deadly to trees.  The KSHB killed some 140,000 trees in the Tijuana River Valley over nine months in 2016 (see http://www.cw6sandiego.com/newly-discovered-beetle-decimates-trees-tijuana-river-valley/), and the PSHB has killed over 1,000 trees on the UC Irvine Campus (http://www.ocregister.com/articles/trees-662428-uci-beetle.html ). 

Of course it gets worse.  The beetles are so small that, to make sure they don't simply fly off from cut wood, you've got to chip the wood to pieces smaller than one inch.  Or you have to seal and solarize the logs for six months.  Grinding a big tree into tiny bits is extremely expensive, as the UCI maintenance people have found. 

There is no good treatment for these beetles, although there is hope for biological control.  This hope comes from the apparent fact that the beetles are rare in their native ranges, and researchers were able to find several possible biocontrol species.  They'd like to run these species through the rigorous USDA certification procedure, but that will take years and cost millions of dollars.  If you want to help with (finding) funding that effort, contact conservation@cnpssd.org.

In the meantime, there isn't any good way to control either of the shot hole borers beyond detecting an infestation early and grinding up the tree that's infested, before the beetles fly and the infestation spreads out of control.

The worst thing that can happen is if people simply cut down infested trees and use the wood as firewood.  You would be right in thinking that burning kills beetles, but unless you bag the logs and take them straight from the bag to the fire, there's a chance for the beetles to fly out.  And for all I know, they'll fly out anyhow as the fire heats them up.  Still, if someone has dozens of avocados dead of disease and it costs thousands of dollars to dispose of the wood safely, then you can see the incentive to simply chop the logs and leave them at the side of the road with a "free firewood" sign.  You'd pick that up, right? (Wrong).

Firewood movement is the main way these pests are spreading.  It's apparently how the KSHB jumped from San Diego to Santa Barbara, and they are concerned it has jumped to San Luis Obispo.  The projected climatic range for the Shot Hole Borers goes all the way up to Tehama County, as well as to Hawai'i, Arizona, and Florida.  They could go a long way if people keep being careless about moving wood.

Indeed, there are several programs, such as dontmovefirewood.org and the State's Burn It Where You Buy It (http://www.firewood.ca.gov/ ) to educate the public about not moving firewood.  I suspect the message is getting out about as fast as the message to not widen trails by riding mountain bikes around puddles, but it's a start.  Dontmovefirewood.org even has a list of 51 pest species nationwide that are being moved through firewood, including dutch elm disease, chestnut blight, emerald ash borer, gold spotted oak borer, sudden oak death, white pine blister rust, and so on. 

Can I convince you not to move firewood, and not to even buy firewood from that ever-so-plucky Boy Scout troop that's selling firewood as a fundraiser?  Thanks in advance.  Now you know why it matters.  Please spread the word.

This, and monitoring trees to see if they suddenly start suffering and dying, are the most important things you can do to help stop the spread of pests.  There aren't good treatments for a lot of plant diseases and pests, and the only way to keep them from radically altering forests is to keep them from spreading.  We failed with chestnut blight, but hopefully we won't fail with our willows.  Or our oaks.

And that's the connection that's bugging me (literally) about the MSCP.  I was invited to join the steering committee for the North County MSCP, and we're hashing through the details of preserve design.  The MSCP is an interesting way to do conservation, because it piggybacks off the needs of a bunch of sensitive and listed species to make a program for preserving wild areas that house a lot more than just those species.  Unfortunately, from my perspective, it also makes it easier for developers to take land outside the preserves in exchange for paying to preserve land, but that's the deal we get as long as we're growing and there's a housing shortage. 

Still, there's a problem with this, and I'm not sure the County planners have fully come to grips with it.  That problem is all the pests, whether it's the KSHB, the gold spotted oak borer (Agrilus coxalis) going after our black and coast live oaks or one of those dozens of Phytophthora species currently in the nurseries turning out to be the next sudden oak death. 

Let me give you an example.  Southwestern Willow Flycatcher (Empidonax traillii extimus) is one of the MSCP covered species.  This is great, because trying to protect it means that we protect all the willow riparian areas.  The problem is if KSHB gets into one of these areas, kills all the willows, and the flycatchers leave or die.  What's the conservation value then?  A developer might not be interested in preserving the area, because it now has no conservation value.  For the MSCP to work, the ecosystem has to be relatively intact.  And to deal with that, all of us have to do our part to slow the spread of all these pests that our global horticultural trade has loosed upon the world.  Keep an eye out, don't move firewood, and when you see something, speak up.  You can contact County Ag, or just email it to conservation@cnpssd.org and I'll put you in touch with the right people.

If you want to be really morbid...well, it's April, and there was a superbloom in the deserts, so I'm not going to be too dark.  But I wonder, sometimes, whether a California species will be the next American chestnut, the next American elm, a common species reduced to rarity or wiped out by an exotic pest we accidentally introduced.  My best catastrophe candidate at the moment is the coast live oak (Quercus agrifolia).  Sure they're everywhere, but they are hosts for both shot hole borers, the gold-spotted oak borer, and sudden oak death (Phytophthora ramorum).  If these were left unchecked, I'm not sure there would be any oaks left in California, and that's a huge blow to ecosystems throughout the state.  Unless and until we get cures for all these pests (don't hold your breath), our vigilance is the best safeguard.  Please do your part.