Thousand Cankers Disease – What Have We Learned J. W. Van Sambeek, Research Plant Physiologist, with the US Forest Service, Northern Research Station, 202 Natural Resource Building, UMC, Columbia, MO 65211-7260 (jvansambeek@ fs.fed.us) and Sharon Reed, Ambrosia and Research Specialist, in the Plant Sciences Division, University of Missouri, Columbia, MO.

Thousand Cankers Disease (TCD) twig are attracted also exist with preliminary studies represents a serious threat to to walnut trees by host tree suggesting Wisconsin are black walnut, an important nut and volatiles and sexual chemicals more susceptible than Missouri and timber tree in the eastern United released by the male. The Oklahoma walnut trees. States. TCD was first described as is carried on beetle bodies and The resistance of Arizona a lethal disease for most walnut is introduced into walnut trees walnut to the G. morbida fungus species in 2009. A webinar when walnut twig beetles probe supports the idea that the fungus is sponsored by the USDA Forest the inner bark, which may or may native to the southwestern US and Service State & Private Forestry not be followed by construction northern Mexico, the native range and Forest Health Protection, of egg galleries. The fungus of Arizona walnut. In addition, the the Walnut Council, and the induces the formation of small wide genetic diversity found among Purdue University Department of round to elliptical shaped cankers G. morbida samples confirms that Entomology on March 28, 2013, depending on susceptibility of the the fungus has been present in suggests we are making progress walnut species (Figure 1). When the US for a long time. The fungus toward knowing the causes of the cankers are numerous enough, most likely spread from its native tree disease, detection of diseased movement of nutrients within the range when beetle-infested walnut trees and causal organisms, origin phloem or inner bark is blocked logs or wood products with bark on of the beetle and fungus, and causing branch decline and were shipped elsewhere. treatments to permit transport eventually tree death. Dusty, white Confirmation of TCD and sale of products from infested produced by the fungus requires positive identification of wood. In the first part of the are formed in egg galleries and the fungus. The fungus is difficult webinar, Simeon Wright, Andrew become attached to the bodies of to identify because the shape Graves, Bruce Moltzan, and Julie most young beetles prior to their of the reproductive structure is Spaulding provided information emergence from the canker and similar to other fungi. Further, about the disease, and, in the bark. many different types of fungi, second part, Dana Rhodes, Norm Black walnut and butternut including other Geosmithia species Dart, Paul Merten, and Dan Kenny are the most susceptible are found on beetle bodies and in spoke about their experiences with species. Species such as northern wood. One study found 19 – 56 TCD in their respective states. The , southern California, different types of fungi on the webinar was recorded and the Persian (English), and little walnut bodies of beetles closely related to entire four hours of presentations have some resistance while Arizona the . To improve are available at the national walnut is the most resistant. identification, investigators in TCD website at: http://www. Hickories and pecans are immune Tennessee are developing a more thousandcankers.com/webinars. to the disease. Although black reliable technique to identify G. php. walnut is susceptible to G. morbida, morbida using its unique DNA TCD is the result of the genes for resistance may be code. The technique is expected walnut twig beetle, Pityophthorus present in the black walnut species. to shorten the process used to juglandis, feeding in the phloem Variation in susceptibility has been identify the fungus when it is grown and subsequent canker formation found among half-sib families on artificial medium. Future by the pathogenic fungus, (seedlings from a single mother modification of the technique may within the tree) and among nut cultivars. In permit rapid identification of the inner bark around these galleries. addition, regional differences may fungus directly from samples of the

THE NUTSHELL, June 2013 15 inner bark collected from a suspect the “I” on a dime (Figure 2). Beetle separated on a gas chromatograph tree. identification requires examination and amount of excitation from The search for an effective under a microscope for two rows insect antenna was measured to chemical treatment for TCD of tubercles on the flattened elytra. detect the most attractive volatiles infected trees continues. In part, Unlike the adult males, females as they emerge. The lure has been finding an appropriate chemical is have a hairy brush (pubescence) patented and is being packaged difficult because walnut produces across the top of their head in packets that can be attached an edible nut. The location partially covered by the thorax. to insect traps to monitor for the of the beetle galleries in the The insect is very prolific and as beetles. The recommended traps tree makes chemical selection many as 100 exit holes have been for monitoring are Lindgren traps even more challenging. Several counted from a 4 inch square piece that consist of four black funnels common systemic pesticides have of bark. Trapping in Tennessee with a wet cup attached to the had limited effect on the beetle showed a consistent peak in adult bottom funnel (Figure 3). Traps are and fungus, most likely because emergence in September and usually hung on poles made from systemic chemicals move mostly October and another weaker peak aluminum conduit set on rebar through the sapwood while the in March, April, and May suggesting driven in the ground. beetle and fungus occupy bark the walnut twig beetle can Adult beetles are clumsy tissues. Research continues on complete two life cycles annually. fliers. When they hit one of the evaluating both systemic and There is good evidence that funnels on a Lindgren trap, they non-systemic pesticides for their the walnut twig beetle is native to fall into the wet cup. Propylene potential to kill walnut twig beetles the southwestern US. The oldest glycol, the pink antifreeze used in and the G. morbida fungus. collections of walnut twig beetle marine or recreational vehicles, is Progress has been made are from Silver City and Paradise, recommended because it will kill in determining if infected logs can dated 1896 and and preserve the insects. Ethanol be a source of TCD and, if so, how 1917. Historical records suggest should not be used because can infested logs be treated so they it is an insect pest of Arizona it attracts ambrosia beetles. can be safely moved and used. walnut on which it can cause Ethylene glycol should not be used Optimum growth of the fungus on death of small branches but does because of its toxicity to animals. artificial medium is 77 to 90 o F; not cause tree mortality. Like the Documents and videos describing but can survive temperatures up associated fungus, there is wide how to set up and monitor to 107 o F and has been isolated genetic diversity within the insect Lindgren traps are available at from frozen logs. Bud Mayfield, indicating it has been around for a http://www.ipm.ucdavid.edu/ a researcher at the USFS Ashville long time. pdf/pestnotes/wtb-trappping. office, has shown that the fungus On black walnut, the pdf and http://www.ipm.ucdavis/ can be isolated from peeled logs; beetles attack branches 1.5 inches pmg/menu.thousandcanker.html. however, the fungus is killed by in diameter but prefer larger In addition, the website at www. heat treatments that raise the branches. On smaller branches, thousandcankers.com has a link temperature of the outer 3/8th inch attacks are usually associated with to the 47- page publication titled of sapwood to 118 o F for 30 to old leaf scars. Tests consisting of Thousand Cankers Disease Survey 40 minutes (higher temperatures cut logs placed in infested areas Guidelines for 2013 (4.5 MB pdf) are needed to kill the beetle). demonstrate that logs remain that has detailed information on Fumigation of infected logs with attractive to beetles for more than using baited traps and photos for methyl bromide at 120 micrograms two months after a tree has been insect and fungal identification. per liter at 40 o F for 48 hours will cut. In an effort to track state also kill the fungus. A male pheromone has efforts, a national database The adult walnut twig been identified from the headspace has been created to document beetle is quite small, about the size volatiles surrounding infected monitoring activities and record of a poppy seed or same length as branches. The volatiles are where walnut twig beetle traps

16 THE NUTSHELL, June 2013 have been deployed. Bruce 2012 to 17 states. Most states walnut trees cut, piled, and burned Moltzan, national TCD program were able to complete their over two days in late February leader, discussed the resulting map cooperative agreements in time to when the beetles were expected that summarized the extent and be part of this monitoring effort. to be inactive. TCD has not been results of monitoring in 2012 which Funds available in 2013 include eradicated as walnut twig beetles is available at http://foresthealth. $333,000 in the Farm Bill after continue to be captured in baited fs.usda.gov/portal. Information as sequestration and any funds not Lundgren traps and declining to negative as well as positive finds spent in 2012. walnuts on nearby property tested has been entered into a national Representatives from each positive for TCD in 2012. database. state with TCD positive trees or Norm Dart, Virginia During the webinar, documented reports of the beetle Department of Agriculture’s plant landowners interested in helping gave a brief description in the pathologist, provided a history of with the monitoring effort by second part of the webinar of how the TCD finds in Virginia. In June placing traps on their land and the disease or beetle was found in 2011 Bartlett Tree Service received servicing those traps were that state and ongoing detection a call about a declining walnut tree encouraged to contact their state efforts. in Richmond and had it checked natural resource or agriculture Dana Rhodes, plant for TCD. With further testing, department directly. However, protection program specialist for additional trees in the surrounding post webinar conversations the Pennsylvania Department of areas were confirmed to have suggest most states would prefer Agriculture, provided a history of TCD. A second find was confirmed that landowners learn to visually the TCD infestation in Pennsylvania. in the summer of 2012 in Fairfax, recognize symptomatic black On 29 July 2011, an arborist in Virginia. Officials have not been walnut trees on their property or in Plumstead submitted branch able to confirm the source of the their communities. In these states, samples from declining black beetles or fungus. Photographs landowners can help by sending walnut trees to the Pennsylvania showing little decline of some TCD local authorities digital photos of Department of Agriculture. The infected trees during a two-year the entire tree, areas of the crown presence of TCD was confirmed on period confirm that the disease can showing symptoms, and close-up 2 August 2011 and Bucks County progress slowly. Current estimates of the leaves. The photos would be was immediately quarantined. between initial infestation and tree used to determine if symptomatic The property owner is an arborist death in Virginia are 5 to 20 years. trees should be further evaluated who also distributes firewood Paul Merten, US Forest for TCD. Limiting the number of and operates his own sawmill Service Forest Health Protection, TCD suspect sites prior to deploying to prepare live edge lumber for provided a history of the TCD traps is important because traps artisans. Six to eight years earlier detections in Tennessee and are expensive, trap evaluation is he had shipped in logs from Chico, North Carolina. The disease was time consuming, and highly trained California for his business. Testing first found in May 2010 when a personnel are needed to accurately of beetles captured in Chico and in friend of employees at the Tree identify walnut twig beetles. Pennsylvania show similar genetic Improvement Center in Knoxville Regardless of your state, contact patterns confirming this shipment submitted samples of declining and your local authorities if you suspect was the likely source of the TCD dead walnuts to Ned Tisserat, the TCD infected trees are present in infested material. State plant pathologist your area. In 2011, ten of 56 walnut who originally isolated and named States have been able trees around the edge of his the fungus. TCD was confirmed to apply to the Farm Bill for TCD property tested positive for after a second set of samples was monitoring funds. Julie Spaulding, TCD. Working with the local fire submitted (Figure 4). Knox and National APHIS coordinator, department and heavy equipment three adjoining counties were indicated $400,000 was made operators, the owner voluntarily quarantined in 2010. Trapping in available through the Farm Bill in without state funding, had all 56 2011 confirmed the presence of

THE NUTSHELL, June 2013 17 TCD in three additional counties. Ohio. Baited traps were placed series of webinars is one sponsored Trapping in 2012 did not result in at 28 high-risk sites across Ohio by The American Tree Farm System. the expansion of the known TCD including the log yard for a veneer Simeon Wright, Paul Merten, and area in Tennessee. The expanded mill in Butler County. In September, Lenny Farlee discussed “Managing number of counties is thought to be eight beetles from collections at the Threat of Thousand Cankers due to better detection techniques the veneer mill were identified. Disease on Your Tree Farm.” It was and not a rapid natural spread of The trapped beetles had been also recorded and can be viewed at: TCD. Currently seven counties shipped in alcohol for identification, http://www.treefarmsystem.org/ are quarantined, meaning walnut so beetles could not be tested for american-tree-farm-webinar-series. trees or their wood products G. morbida to confirm TCD. The To find the webinar, find “Check along with hardwood firewood mill had received a shipment of on our Archives” and select the cannot be moved outside these walnut burls from western April 18th presentation. While at counties. The eleven surrounding as late as July 2012. At the time of this website, you may also want to counties are listed as buffer the quarantine, there were 1516 view the March 15, 2012 webinar regulated areas, meaning walnut walnut logs in the yard and under on “Managing for Black Walnut” by trees and products can be move a compliance agreement, 710 of Mel Baughman and Lenny Farlee. between buffered counties and into these logs were processed into It is a very good introduction to quarantined counties, but not taken veneer and the rest fumigated or site identification, establishment back out again from quarantined burned. Detection of the beetles and plantation management of counties. In 2013, Tennessee will occurred too late in the year for black walnut for timber and/or nut put out 70 baited traps across inspection of the fifty walnut trees production. the state with one trap in each in areas surrounding the mill, which Figure Legends quarantined county to confirm the will be monitored with more than emergence pattern and two traps 20 baited traps during the 2013 Figure 1. —Exposed walnut twig in each buffer county to continue summer. beetle egg galleries and fungal monitoring the extent of the In summary, the interest in cankers responsible for TCD in the disease. TCD is high as over 250 people from inner bark of walnut branches. In 2012, trees infected 26 states and Canada participated (Photo from Colorado State with G. morbida were found in in the March 28 live online webinar. University TCD Recovery Plan) North Carolina’s Great Smoky The webinar was recorded and Mountains National Park. North can be viewed on the national Figure 2. —Size of an adult walnut Carolina employees identified 151 TCD website at: http://www. twig beetle compared to pencil tip TCD-suspect trees. No walnut thousandcankers.com/webinars. (Photo by Ned Tisserat). twig beetles were detected but php. The follow-up webinar on April G. morbida was isolated from 25 described survey protocols, field Figure 3. —Baited four funnel two suspect trees in late August identification of thousand cankers Lindgren trap attached to aluminum 2012 and its identity confirmed by disease, and an FHTET demo of conduit (Photo by Steve Seybold, molecular testing. These trees are survey database entry. A third US Forest Service). located along the edge of different webinar on May 30 will include campgrounds in open woodlands an update of current research and Figure 4. —Black walnut tree within the park where it borders methods as well as discuss plans for in Knox County showing TCD Tennessee. public outreach plans and outreach symptoms (Photo by Bruce Moltzan, Dan Kenny, Ohio needs. The latter webinars will also US Forest Service). Department of Agriculture, be recorded and made available on described the events leading to the above website. trapping of walnut twig beetles in An alternative to the above

18 THE NUTSHELL, June 2013 TCD - Figure 1.

TCD - Figure 2.

THE NUTSHELL, June 2013 19 TCD - Figure 3.

TCD - Figure 4.

UPDATE: Dan Kenny reported in early June that walnut twig beetles have been captured this spring in 9 of 26 traps in Butler county most likely from walnut trees around the veneer mill where beetles were captured in 2012. The quarantine has now been expanded to include all of Butler county.

20 THE NUTSHELL, June 2013