Great Article on Invasive Shot Hole Borer

The Invasive Shot Hole Borer (formerly called the Polyphagous Shot Hole Borer) is still a threat to native and introduced trees here in California, and although in some cases it seems to be mellowing out just a little bit, it still has the capability of getting worse -especially during the curent severe drought. Here is an article by Rosi Dagit that summarizes that current state of affairs with this pest and also some opportunities to be involved in citizen science efforts to keep track of it.

Tree limb infested with Invasive Shot Hole Borer

Discoloration on bark indicating Shot Hole Borer attack

The Invasive Shot Hole Borer

Something Bad is Happening to Our Magnolias, But There May Be Some Hope

In the last several years I've noticed that many Southern magnolias (Magnolia grandifloras) in the greater Los Angeles area are taking a turn for the worse. They're losing branches, their canopies are thinning and they are, in general, looking terrible. For example below is a picture of a southern magnolia cultivar 'Samuel Sommers' in 2012 (on the left) and just recently (on the right). Notice in the recent photo that only 50-60% of the trees canopy is left. The side-by-side photo below is one of the milder examples of how Southern magnolias have declined over the past several years.

Magnolia "Samuel Sommers" left: in 2012, right November 2018

Below also are some examples of Magnolia grandiflora street trees growing in an Alhambra neighborhood (there is nothing special about Alhambra except that they seem to have a large amount of M. grandiflora planted as street trees).

Magnolia grandiflora planted as street trees in Alhambra California

Magnolia grandiflora planted as street trees in Alhambra California. Notice the dead branches appearing randomly in the canopy of the tree, a process called 'flagging'. 

These Magnolia grandiflora trees once had much larger canopies, with some of the trees canopies shrinking to 1/2 their previous size.

What's causing these once beautiful, magnificent trees to decline? There doesn't seem to be any one cause, but there are many culprits. The number one culprit is that this tree is like a fish out of water here. Native to the deep south and south eastern portions of the United States, Magnolia grandiflora thrives in cool, but not snow covered winters and hot, humid, and rain punctuated summers that its native range provides. It does do well here it it has plenty of humidity and water, however these conditions are becoming harder to maintain. But climatic differences aren't the only culprit.

Magnolia grandiflora suffers from a significant pest and two very damaging diseases. The pest is the polyphagous shot hole borer (PSHB), for which Magnolia grandiflora is a host.  The diseases are Xylella and Botryosphaeria 

But most of the damage to Magnolia grandiflora and many other street trees can be attributed to what is essentially a very bad interpretation of a famous landscape designer's radical new idea. Frederick Law Olmsted, who previously had designed Central Park on Manhattan Island, New York, was commissioned to design one of the first planned suburbs in the United States, Riverside Illinois. His plan specified walkways and trees lining the avenues of the community. These became so popular that the idea of tree lined urban and small town streets became an archetype of America and a specification of many an urban plan. Unfortunately this vast majority of these Law Olmsted imitators did not specify the same amount of space between street and sidewalk as Law Olmsted -10 feet between the two, ample room for the the roots of most trees.

The planting of trees in spaces much smaller than the almost 300 square feet than Law Olmsted gave the Riverside trees lead to an entire nation with millions of trees stressed out. The idea of tree lined streets took off, but the idea that those trees required adequate space to set out their roots did not.  And although smaller trees like Privets and Crepe Myrtles can be planted in the small spaces between urban and suburban streets and sidewalks, larger trees planted in such small spaces are basically doomed.

So though there may not be hope for the thousands of Magnolia grandiflora planted as street trees here in the Southland, there may be some hope for the tree if it is planted with plenty of room (and regular watering) to let it grow. In fact just behind the two waning Magnolia grandifloras located just west of the Crescent garden here is a compact variety of the tree that seems to be thriving, Magnolia grandiflora 'Victoria'. Although there is a small amount of shoot dieback on the tree it is relatively healthy. The reason? I'm not completely sure, however the tree is surrounded by other trees and is next to a lawn, this would mean plenty of water and humidity. But the one thing I think is making a big difference is that the tree is free and clear of lawn or any other kind of plant underneath its canopy and the only thing there is a thick layer of its own leaves. I can't tell you the number of times I've observed evergreen trees doing better because a thick mulch of their own leaves was permitted to remain underneath their canopies.

Magnolia grandiflora 'Victoria'
Notice that the canopy of this tree is healthy and thick compared to the Magnolias pictured above. 

Closeup of Magnolia grandiflora 'Victoria'  

Substantial mulch layer under the canopy of Magnolia grandiflora 'Victoria' composed of its own leaves.  

The mulch layer of leaves is at least 3-4 inches deep. 

Inexpensive 3D Trap Aids in the Detection of PSHB

There is finally some good news coming out of efforts to control the Polyhphagous Shot Hole Borer (PSHB). With over 200 common landscape and native trees being attacked by this pest, and over 36 host trees it can breed in, the term 'apocalyptic' is hardly an exagerated one for this pest. Up until the last 6 months things were looking kind of grim, with only regular trunk spraying of contact insecticides being an effective control. Because of the huge list of hosts and trees under attack and non-hetrogenous nature of the ornamental trees (good scientific experiments require multiple samples of uniform subjects, something hard to find with the mature trees the beetle attacks), progress in controlling the beetle has been slow. However the use of 3D printing has allowed custom traps specific for this beetle to manufactured en mass for deployment in the field. These custom traps will allow researchers to better determine the effectiveness of prospective treatments in the field. Also, at least one parasite specific for PSHB may have been discovered in Taiwan. Stay tuned!

California Landscape Contractors Fund Polyphagous Shot Hole Borer Research

As the grave nature of the consequences of the current Polyphagous Shot Hole Borer infestation become clearer another organization with a stake in plants the pest attacks are donating money for research into methods to control it. Up until now the California Avocado Commission has been the biggest donor, but recently another organization that might have much more to lose, the California Landscape Contractors Association, is funding research. With the majority of the plants being attacked by this pest being important elements in landscape design here, this funding makes good sense for the organization whose members rely on them as the fundamental building blocks of their industry.

Links for May 1st CAPCA Talk

PSHB Links

1.    CISR: Polyphagous Shot Hole Borer

2.    Polyphagous Shot Hole Borer - Pest and Disease Threats to Southern California Oaks

3.    Polyphagous shot hole borer | Don't Move Firewood

4.    Identifying the Polyphagous Shot Hole Borer Beetle | California Avocado Commission

5.    Have you seen a Polyphagous shot hole borer lately? - Green Blog - ANR Blogs

6.    Plant Disease - 97(7):938 - Abstract

7.    ARS : News & Events

8.    caforestpestcouncil.org/wp-content/uploads/2008/07/Polyphagous-Shot-Hole-Borer-update.pdf

9.    ARS : News & Events

10.Mycologia Article about PSHB Associated Fusarium: Sign In

11.Officials Warn Citizens To be on Lookout For Invasive Pests - Government - Glendora, CA Patch

12.UCR Today: New Invasive Beetle-fungus Complex Found in Riverside and San Diego Counties

13.CISR: Redbay Ambrosia Beetle and Laurel Wilt

14.Importance | Ambrosia Symbiosis

15.Ambrosia Symbiosis

16.Review of Bark and Ambrosia Beetles in California: essig.berkeley.edu/documents/cis/cis16.pdf

17.Review on Effects of Climate Change on Ambrosia Beetle Populations: Review - Journal of Asia-Pacific Entomology - Tom 14, Numer 2 (2011) - Biblioteka Nauki - Yadda

18.Winter 2013 PSHB Update: www.californiaavocadogrowers.com/sites/default/files/documents/2013 Winter PSHB Update.pdf

19.Update on PSHB Vietnamese Connection: PSHB Exploration in Vietnam | California Avocado Commission

20.CAC Research Update: Research | California Avocado Commission

21.Eskalen Lab: Fusarium Dieback / Polyphagous Shot Hole Borer: Includes Complete List of Reproductive Hosts

22.Pictures of PSHB/FD from Akif Eskalen

23.Eskelan Report on Iseali PSHB Infestation

24.Article on Huntington Botanic Garden Participation in PSHB Research: huntingtonblogs.org

25.Thermal Imaging and Pest Control: IR Thermography for the Pest Management Professional

Red Haired Pine Bark Beetle Links

26.Red-Haired Pine Bark Beetle | Don't Move Firewood

27.Red Haired Pine Bark Beetle Handout: https://fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5332562.pdf

28.Research Findings Shed Light on New Urban Pest of Pine Trees

29.US Forest Service Handout on Red Haired Bark Beetle: www.na.fs.fed.us/spfo/pubs/pest_al/redhaired/red_haired_bark_beetle.pdf

30.Western Bark Beetles - US Forest Service Research & Development

31."Climate Change and Bark Beetles of the Western United States and Canada" by Barbara J. Bentz, Jacques Régnière et al.

32.IPM for Home Gardeners Handout on Bark Beetles: ucanr.edu/sites/sjcoeh/files/77067.pdf

Global Warming Ambrosia Beetle Link Paper

Polyphagous Shot Hole Borer Links

PSHB Online Resources

UCR PSHB Page

CISR: Polyphagous Shot Hole Borer

University of California Agriculture and Natural Resources PSHB Page

Polyphagous Shot Hole Borer - Pest and Disease Threats to Southern California Oaks

Don't Move Firewood Page on PSHB -Contains Native and Non-native Host List

Polyphagous shot hole borer | Don't Move Firewood

California Avocado Page on PSHB

Identifying the Polyphagous Shot Hole Borer Beetle | California Avocado Commission

Article on Initial Public Conference on PSHB Held at UCR in August of 2012

Have you seen a Polyphagous shot hole borer lately? - Green Blog - ANR Blogs

UCR Power Point Presentation on Polyphagous Shot Hole Borer

caforestpestcouncil.org/wp-content/uploads/2008/07/Polyphagous-Shot-Hole-Borer-update.pdf

UCR Today (UCR's online magazine) Article on PSHB -Includes Host List

UCR Today: New Invasive Beetle-fungus Complex Found in Riverside and San Diego Counties

UCR Page about Redbay Ambrosia Beetle

CISR: Redbay Ambrosia Beetle and Laurel Wilt

Study Group for Fungal-beetle Symbiosis

Ambrosia Symbiosis

Article on Native Bark and Ambrosia Beetles

essig.berkeley.edu/documents/cis/cis16.pdf

Infrared Imaging Trade Group Page's Article on Thermal Detection of Insects

IR Thermography for the Pest Management Professional

The Unseen Arboretum (Amazing Images)

Recently the FLIR corporation was kind enough to lend us one of their thermal imagers in order to determine if they could detect the level infestation of a new and dangerous pest here, the Polyphagous Shot Hole Borer. The images produced by the machine, a FLIR T440, are amazing. At night the trees seem to glow (even though the temperature differences are small, the coloration that is done by the FLIR camera highlights them dramatically).  Initial analysis of the images seem show a correlation between the images and infestation levels of the pest. 

A FLIR T440 image of shot hole borer infested oak trees -the differing colors on the trunks are due to temperature differences. 

The spots on this oaks' trunk may be due to shot hole borer activity. 

At night the trees at the Arboretum glow in the eyes of the FLIR T440 thermal camera. 

The bright yellow color indicates hotter areas then those areas showing orange or purple. 

A liquidambar tree in the Meadowbrook section as seen through the eyes of the imager.  

Trees on Tallac knoll as seen through the FLIR T440.

Polyphagous Shot Hole Borer in the News!

Looks like television news is starting to discover how bad PSHB is. 

PSHB Infestation at Local Park.

California native sycamore showing rusty stains and small holes indicative of the Polyphagous Shot Hole Borer. 

A large local park in the San Gabriel Valley has an extensive infestation of PSHB  that has killed or damaged what appears to be 10% of its tree canopy. The two most affected plants are California sycamore (Platanus racemosa) and White alder (Alnus rhombifolia). The extent of this infestation here in the San Gabriel valley is quite significant and could change the the way we use trees here.

Alder bark showing PSHB hole and staining.

One of the things that might be exacerbating this infestation is the long period of drought we are currently in. There has been only one year of normal rainfall here in the L.A. area since 2005. Ground water levels are low and this can put huge amounts of stress on large trees that rely on groundwater such as Alders, Sycamores and Oaks. Extra water may not be the answer because it might not be possible to supply the amount needed for large trees solely through irrigation.

White alder 3/4 dead from PSHB

One of the things that might have to change is the tree density here. If you look at historic photos of Los Angeles you notice large areas of treeless plains. There is a reason for this; these areas were mostly grasslands and could not support large trees without irrigation.

California native sycamore infested with PSHB

Cottonwood tree growing in undeveloped river bottom showing possible PSHB infestation.