A Plague On Both Your Houses

(The main photo is of a Flat-Head Borer removed from a Ponderosa Pine)

There are some pests and pathogens that will deform, devalue, or downright decimate your bonsai.  It is rare that I see anything written on the blogs  so I felt it time to devote some keystrokes toward the matter.  Ever since my first of a few plant pathology courses at The University of Georgia, plants have not been viewed in the same fully joyous light.  The question “What the hell is this going to get?” is unfortunately one of the first things I ask myself when meeting a new cultivar or species of plant.  While every species and even cultivated variety of plant has their own issues, the purpose of this post is to highlight a few of the most nasty things to watch out for.   Rare plants are often rare for a reason…..  This post will focus on deciduous and broadleaf evergreens.  Perhaps an “evergreen conifer pro” and a “tropical pro” will put something out soon.  If nobody steps up on the conifer front, I’ll get to it eventually.  Many pests and pathogens are species specific and buying a chemical suitable for mites may not kill the mites you have.  General terms like “root rot” just don’t get to the root of the matter.  Send out soil samples to labs and know what you have for sure; even in a post-mortem situation.

Culprit #1:  Erwinia amylovora (Fire Blight)

Fire blight is a bacterial infection that affects a number of species in the Rosacae Family.  Some, like Cotoneaster and Pyracantha, seem more susceptible as they are floriferous.  This little bastard can be transmitted by pollinators through the pistil of a flower, through stomates and lenticels, insect feeding sites, pruning points, or wound site.  Generally the first thing to be affected is new growth or flowers.
Then come death of the twig and eventually branches and trunks.  Once a plant is infected, it can be hard to get rid up.  It is best to cut well below the visibly affected area as the bacteria could be a foot further down the plant.  For full details I refer you to this site HERE.  Bordeux mix or Copper fungicides can be applied.  From experience, early applications in late Winter repeated until late Spring may be necessary if it’s a particularly wet year.

Genus known to be affected are:   Malus, Cydonia, Psudocyodonia, Pyrus, Spirea, Cotoneaster, Pyracantha, Crataegus, Rubus, Sorbus, Chaenolmeles, etc.  If it has a five-petaled flower, it can likely be affected.

The weather and local infection chords are major players in new infections.  A landscape plant nearby could affect your bonsai if bees, flies, aphids, etc. bring the ooze from infections to your benches.




Culprit #2:  Nectria cinnabarina (Coral Spot)

Also known as Coral Spot Canker, comes from the Latin base “red killer”.  It is a facultative saprophyte, so is often found on dead tissue like branch stubs that have died back.  When it invades living tissues through lenticels or fresh wounds from pruning or insect damage is when it causes problems.  This fungal pathogen seems to be more prevalent in Europe but I’ve seen it in Tennessee and on plants shipped in from Oregon.  My first encounter was with a pre-fabricated European beech hedge project I made.  The group of 50 trees were pruned annually to form a low wall when installed.  About 20 had beige lesions forming on twigs and in some cases the trunk.  IMG_1848Two weeks later, neon pink fruiting bodies covered the area and all affected areas died back.  Basically, a few likely had it and pruning the whole group caused them all to eventually get it.  My research at that time (2008) yielded exactly the same results as last week; there’s nothing to cure it which makes it scary as hell.  It seems that disposal of afflicted plants is best via bagging or burning for severe infestations, but cutting off below affected areas with repeatedly sterilized pruners can be effective if the fungus is not present on the trunk(s).  You do not want to have infected plants producing spores in Spring.  The fungus can also spread from rain splash off of dead tissue on the ground or in containers.  It can stay on necrotic tissue for a while.

Genus affected are:  Acer, Tilia, Fagus, Aesculus, Carpinus (I’ve seen it on Carpinus japonica but not Korean hornbeam), and Juglans.

Trunk of a Carpinus japonica with a severe infestation of Coral Spot about to pop.






Culprit #3:  Rhizoecus americanus (Cypress Root Mealy Bug)

This one affects Bald and Pond Cypress roots.  Trees decline in vigor and new growth in Spring will be an “off color”.  Foliage can also emerge in a less that beautiful way.  My experience has been limited to seeing it in Florida’s collected Taxodium; either collected material for sale or established bonsai made from collected material.  Products containing Imidacloprid can be applied to kill them.

root-mealybugsPersonally, I’d drench the root system during repotting and remove some media to make sure you get them even though you’re applying a chemical that has systemic properties.






Culprit #4:  Cnestus mutilatus (Camphor Shot Borer)

With a specific epithet like “mutilatus”, there is cause for worry……  This one seems to be popping up all over the country lately.  I’ve seen it on Gingko biloba and Metasequoia glyptostrobiodes.  Both groups came from a grower in Oregon and were fully dormant.  Shortly after the buds started to swell, I notices dozens of holes in the trunks of almost every tree. Foliage came out smaller than normal and very slowly.  A few months later I spotted it on a fairly large Gingko in a garden.

For those of you who will check the national maps for where this and any other pest or pathogen has been found, keep one thing in mind.  If you were a wholesale or retail business that spotted an issue, would you report it?

Caphor-Shot-Borer-300x225Presence of Fire Ants for example, requires every plant shipped outside of the “fire ant zone” to be treated with expensive chemicals before shipment.  Do you think everyone is reporting outbreaks and infestations?  As a native to Georgia, I grew up with fire ants.  When working in Nashville, where fire ants were not supposed to have naturalized, I “never saw any”……

The photo to the right is of Camphor Shot Borer that attacked a gasoline can attracted by the ethanol.

Attacks have been prompted by researchers on black walnut, golden raintree, red maple, sweetbay magnolia, tulip poplar, and white oak by injecting tree trunks with ethanol. Ethanol is naturally produced by stressed trees and is used by ambrosia beetles like CSB to locate trees suitable for attack.


These are just four pests to watch out for.  My background allows me to spot these types of pests and diseases as they start by how they affect plants.  Some, like borers, can be stopped in their tracks (or galleries).  Some of the terminology I’ve used in this post is a bit heavy but I’m hoping to prompt you to do some research on the matter so you are prepared.  Just because the cover or title of a publication doesn’t say “BONSAI” doesn’t mean you cannot benefit from it.  Quick web searches of pathogens can yield local findings from university and state sponsored research.  For those of you feeling a bit squeamish, I’ll leave you with a nice photo of a happy tree : ).

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