Nightmare on Walnut Street: Thousand Cankers Disease as an Emergent Threat to Juglans

Nightmare on Walnut Street: Thousand Cankers Disease as an Emergent Threat to Juglans Whitney Cranshaw Colorado State University Presentation for the International Society of Arboriculture Conference Chicago, IL July 27, 2010

Thousand Cankers Disease (TCD) An Insect/Fungal Disease Complex affecting some Juglans spp.

A fungus Geosmithia morbida A beetle walnut twig beetle

Jim LaBonte Walnut Twig Beetle Pityophthorous juglandis Jim LaBonte

Adults enter trees and excavate galleries

An egg gallery is produce along which eggs are laid

Larval feeding produces a loose network of meandering tunnels in the cambium

A full grown larva, preparing to pupate.

Teneral adults and pupa, covered with Geosmithia spores

Adults emerge through minute exit holes

The Pathogen - Geosmithia morbida

Walnut twig beetles emerging from infested trees are contaminated with spores of the fungus

Geosmithia is introduced into wounds made by walnut twig beetles

Growth of the fungus beyond the inoculation site creates a dead region (canker) in the cambium.

Multiple cankers produce girdling that seriously restricts movement of nutrients.

Walnut twig Death beetle exit holes by TCD Working Hypothesis Girdling from cankers (and bark beetle tunneling) restricts movement of nutrients. Trees weaken as stored energy reserves become depleted. External symptoms develop in end stages of infestations Trees ultimately die from energy depletion.

Flagging symptoms emerge in end stages of 1000 cankers on black walnut

TCD Symptoms in July 2009 (Olney Springs, CO) Tree is now dead

Foliage wilting may occur rapidly on TCD-compromised limbs

September 2008 June 2008 June 2009

Origin of Thousand Cankers Disease

The walnut twig beetle was originally described (1928) from Arizona walnut, Juglans major. Great picture by Jim LaBonte, OR Dept. Agriculture! Original collections of the beetle were made in 1896.

Published distribution of Arizona walnut

Arizona walnut (Juglans major) Host associated with original descriptions of the walnut twig beetle

Arizona walnut is a common species found in canyons and along riverways

In 2008-2009 surveys, walnut twig beetle was repeatedly found in Arizona walnut at several sites in NM and AZ

Walnut twig beetle in AZ walnut functions as a typical Pityophthorus species of twig beetle. Attacks are normally limited to small diameter branches and function as a form of natural pruning.

Progression to fullblown Thousand Cankers Disease has not been observed in AZ walnut.

Southern California walnut Juglans californica Another native host of walnut twig beetle?

California records for walnut twig beetle date to the late 1950s (Los Angeles County)

Geosmithia morbida is also likely to be a native fungus.

The Geosmithia fungus is has been found consistently associated with the tunnels and frass of walnut twig beetles regardless of Juglans spp. or site of collection.

Evidence suggesting Geosmithia morbida is a native fungus The fungus is consistently associated with walnut twig beetle wherever walnut twig beetle occurs The genetics of Geosmithia strains collected over broad geographic areas appear to be showing diversity (data limited) No apparent genetic bottlenecks Geosmithia morbida is a warm temperature fungus Consistent with a warm climate of origin

Progression to fullblown Thousand Cankers Disease has not been observed in AZ walnut.

Resistance to Thousand Cankers Disease may often result from differences in susceptibility to Geosmithia morbida Canker formation in black walnut Canker formation in Southern California walnut

How did this happen? - Somehow the beetle jumped hosts.

Colorado Potato Beetle (Jumped from buffalobur to cultivated Solanum then moved across US and into Europe)

Apple Maggot Jumped from hawthorn (Cratageus) to apple (Malus)

Jumped from wild cotton in Mexico to cultivated cotton and spread throughout the US Cotton Belt. Boll Weevil

How did this happen? - Somehow the beetle (and fungus) jumped hosts.

Walnut Twig Beetle Range Expansion Big Bang or Buttheads

Spread of walnut twig beetle through the western states involved human transport of infested wood products

What is Thousand Cankers Disease? Black walnut Arizona walnut

A canker producing fungus (with vector) + A susceptible host (black walnut) =

A canker producing fungus (with vector) + A nonsusceptible host (Arizona walnut) =

Thousand Cankers is a different disease in different Juglans hosts

Thousand Cankers Disease (TCD) An Insect/Fungal Disease Complex affecting Juglans spp.

Either the beetle or the fungus indicate presence of thousand cankers disease

A Brief History of the Discovery of Thousand Cankers Disease

Unexplained decline of black walnut in eastern Colorado has been observed since about 2001

The first published association of walnut twig beetle with black walnut in decline occurred in the Espanola Valley area of northern New Mexico (2002)

In New Mexico and Colorado the decline of black walnut and the involvement of walnut twig beetle was originally assumed to be associated with drought.

My personal epiphany: Idaho Hort Expo, January 2008 #1 topic of audience concern involved black walnut die-offs Idaho 2004 record of walnut twig beetle; associated with die-off of black walnut in Boise- Meridian area (Frank Merickel)

Other Recent New State Records for Walnut Twig Beetle Idaho 2004 record; associated with die-off of black walnut in Boise-Meridian area (Frank Merickel) Utah Widespread die-off occurred in late 1990s in Provo area. State records from that time period (1996). State record of a single beetle August 22, 1988 from Provo. (Shawn Clark, Diane Allston)

Other Recent New State Records for Walnut Twig Beetle Idaho 2004 record; associated with die-off of black walnut in Boise-Meridian area (Frank Merickel) Utah Widespread die-off occurred in late 1990s in Provo area. State records from that time period (1996). State record of a single beetle August 22, 1988 from Provo. (Shawn Clark, Diane Allston) Oregon Common in 2004 traps samples in the Dalles area. Review of samples identified 1997 sample from Portland (Jim LaBonte) WA Recovered from symptomatic trees in Prosser area (2008)

The Big Question: How can a little twig beetle be killing healthy trees???

Pityophthorus bark beetles are collectively known as twig beetles because they normally restrict damage to small diameter twigs.

Geosmithia morbida a fungus that is pathogenic in certain walnuts

Thousand Cankers Disease was first formally described (i.e., published in refereed journal) in August 2008

Areas with Walnut Twig Beetle Confirmed - 2009 2008 1997 2003 1988 2004 1959 1958 1896

Native Range of Juglans nigra (Black walnut)

Can Thousand Cankers be Contained in the West?

2009 Colorado Juglans Survey Goals Locate all Juglans spp. in Colorado east of the Continental Divide Do preliminary assessment of TCD incidence Do follow-up on suspect trees in edge areas

Preliminary Assessment Concentrate survey to find edge of infestation within state Rank trees for TCD 0 No symptoms 1 Some symptom (e.g., old dieback) worthy of note, suspicion 2 Symptoms highly suspect for TCD Follow-up on suspect trees with ground sampling

Some lessons learned in 2009 survey Black walnut trees in Colorado tend to be concentrated in older neighborhoods Best time for finding trees was mid June- August Best time for identifying symptoms is late June through August TCD-related flagging develops with summer stresses Other sources of flagging become prominent in late summer

Thousand Cankers Colorado hot spots - 2010

Thousand Cankers NOT spots - 2009

Thousand Cankers presents a new paradigm of a tree disease

Either the beetle or the fungus indicate presence of thousand cankers disease

Thousand Cankers emerged as a tree killing disease when it moved from native resistant hosts into susceptible hosts

Symptoms of Thousand Cankers Disease develop following sustained introductions of Geosmithia by walnut twig beetles in susceptible hosts.

Dutch elm disease has different epidemiology

DED fungus grows in and results in the plugging of the xylem.

Thousand Cankers Disease is associated with the cambium, and does not move systemically in the xylem or phloem.

Root grafting is a concern with Dutch elm disease

Dutch elm disease killing row of street trees

Thousand cankers disease killing black walnut in Olney Springs

Tree death from Thousand Cankers results from overwhelming numbers of individual infections not a single inoculation

Good News: It takes a long time (Decade? More? A bit less?) for a tree to die following initial colonization by walnut twig beetles.

Visual symptoms of Thousand Cankers only develop in the last 2-3 years of the life of the tree.

Bad News: By the time symptoms appear it can be assumed that the walnut twig beetle is generally distributed in the area.

Walnut twig beetles readily breed in logs

Two 18-in logs produced 23,040 beetles in one year after being cut

Bad News: Walnut wood from symptomatic trees or trees cut due to TCD infection is extremely infectious.

A walnut log in Denver waiting for Uncle Benny from Chicago

Wood salvaged from TCD-affected trees is extremely contagious

Beetle infested black walnut from Boulder area with bark attached as advertised on the internet

What about chipping?

Walnut twig beetles were able to complete development in larger pieces following chipping

Factors Affecting Course of Thousand Cankers Disease Resistance of host Species differences Vigor of host Available energy reserves Amount of local inoculum Environmental conditions

Native Walnuts (Juglans spp.) in North America Black walnut (J. nigra) Butternut (J. cinerea) Northern California walnut (J. hindsii) Southern California walnut (J. californica) Arizona walnut (J. major) Little walnut (J. microcarpa)

Relative Resistance of Juglans to Thousand Cankers Disease Preliminary Observations Highly Susceptible Black walnut (Juglans nigra) Moderately Susceptible Northern California walnut (J. hindsii) Moderately Resistant Southern California walnut (J. californica) Persian/English walnut (J. regia) Highly Resistant Arizona walnut (J. major) Little walnut (J. microcarpa)??

Bad News: Prospects for effective chemical control of walnut twig beetle are poor.

Drenching branch sprays for walnut twig beetle

Foliar treatments? The beetle attacks all areas of the tree. Attacks can occur over a period of several months (mid-april through mid-september). Establishment and maintenance of coverage will be very difficult.

Soil treatments and Walnut Twig Beetle - Anecdotes Imidacloprid may assist in slowing spread of walnut decline if it is applied prophylactically Dinotefuran, dimethoate may assist slowing spread of decline but trees are not saved Treatments are not legal on nut-bearing trees

Systemic insecticide soil drenches/ trunk injections? The fungus grows ahead of the beetle. Cankered areas may prevent movement of insecticide to the beetle feeding site.

Thousand Cankers Management & Pesticides What kind of crop is black walnut?

Pesticides Used on Black Walnut Must Probably legal Imidacloprid Chlothianidin be Consistent with Labels for Nutbearing Crops Not apparently legal for use on black walnut Dinotefuran Abamectin Enamectin benzoate

Bad News: Prospects for effective control of walnut twig beetle are poor. Insecticides may slightly slow, but will not stop the progress of TCD.

Key to Thousand Cankers Management Contain the Spread!!!!!

Forestry emphasis in the western states - #1 priority is to prevent the movement of infected wood to new areas All wood from TCD affected trees must be retained locally

A Juglans Quarantine Would affect logs/wood with bark intact Would not need affect Milled wood without bark Logs that have sufficiently dried so live beetles cease production (3 years?) Kiln-dried wood (questions remain about reinfestation potential) Nuts

States with Existing or Proposed TCD Quarantines Missouri Iowa Kansas Michigan Indiana Nebraska

Value of the Juglans Quarantine Announcement of quarantine vastly increases public awareness of issue severity National quarantine would empower state and local officials to develop effective containment actions

Where is APHIS on this issue? Current decision of this agency is that it is not their problem since insect is native to the United States

Emerald ash borer is to Osama bin- Laden. An analogy for regulatory people

as Walnut twig beetle is to Timothy McVeigh An analogy for regulatory people

What I said last month. Good News: Walnut twig beetle has likely not yet reached the native range of Juglans nigra (we think).

July 20, 2010 Very, very bad news: Thousand cankers and walnut twig beetles found in the center of the native range of Juglans nigra Note: The local foresters thought that the trees were suffering from drought stresses

Thousand Cankers has now breached the geographic barrier of the Great Plains!!!!

Good News: It takes a long time (Decade? More? A bit less?) for a tree to die following initial colonization by walnut twig beetles.

Bad News: By the time symptoms appear it can be assumed that the walnut twig beetle is generally distributed in the area.

Implications of TCD Finding in Native Range There are now no ecological or geographic barriers that will prevent TCD spread throughout the entire range of Juglans nigra Natural spread will be slow (comparably) but inexorable Containment through restrictions on movement of walnut wood products may slow spread

Foresters are the Front Line in the Detection of Thousand Cankers Disease! Investigate symptomatic trees Locate limbs with evidence of walnut twig beetle Trap walnut twig beetle

Look for symptomatic trees with flagging

Black walnut showing conspicuous flagging August 2009

No yellow flagging yet apparent June 17, 2010

Limbs with previous flagging do show dieback

Dieback and flagging may be due to: Hail injury Storm damage Fox squirrel girdling Herbicide injury

Remove flagging limb and look for evidence of walnut twig beetle and Geosmithia-produced cankers

Either the beetle or the fungus indicate presence of thousand cankers disease

Geosmithia morbida can be cultured from cankers, beetles, galleries, frass

Look for signs of the walnut twig beetle on dead limbs

Walnut twig beetle exit holes may be visible in limbs, particularly with smooth bark.

Walnut twig beetle trunk entry wounds with some weeping

Trapping

Bad News: No effective traps for walnut twig beetle have been identified. Attractants with limited activity are in early development.

The walnut twig beetle is a minute bark beetle. Great picture by Jim LaBonte, OR Dept. Agriculture! It is one of few Pityophthorus species that develop in hardwoods.

There are features that are useful for identification of the walnut twig beetle

TCD Training Workshops Many states are now trained in TCD diagnosis

An Interim Web Site for TCD information Department of Bioagricultural Sciences and Pest Management Colorado State University Click on Extension and Outreach