(Appendix C, exerpted from: Forest & Shade Tree Insect & Disease Conditions for Maine:  A Summary of the 2008 Situation)

An Eradication Plan for Larch Infected with the Larch Canker Pathogen (Lachnellula willkommii) in Brunswick, Cumberland County, Maine

William D. Ostrofsky

Forest Pathologist

Maine Forest Service

168 State House Station, Augusta, Maine 04333-0168

Introduction:  In 2007, the fungal pathogen that causes the disease commonly known as larch canker was found infecting several larch trees on property of the Brunswick Golf Club.  Pathogen identification was confirmed by Dr. John McKemy of APHIS on November 30, 2007.  The pathogen is currently under Federal Quarantine in the Downeast and mid-coastal portions of Maine.  A map of the quarantine areas is presented elsewhere in this Annual Summary Report. 

The Brunswick discovery was a new Town and County record for presence of the disease in Maine.  Because the infected trees occur outside the current quarantine area, one of two efforts needed to be undertaken to prevent further spread of the disease, and to limit risk to both nearby and distant larch resources.  The quarantine could have been expanded to include the new infestation, or this recently recognized infestation could be  eradicated. 

Survey:  To determine the appropriate action, an intensive survey was conducted during the spring and summer of 2008 to determine the extent of the infestation and the location of any nearby larch resource that may be at risk. 

The area selected for intensive survey is bounded by Interstate 295, from the Androscoggin River to the Exit 28, southbound ramp to the Northwest; by US Route 1 from the Exit 28, southbound ramp to the River Road on the South; and by the Androscoggin River to the Northeast.  The area is approximately 670 acres in size. The entire area was scouted for the presence of larch (Larix spp.), the susceptible host species.  GPS coordinates were obtained for all identified larch.

Inspections of individual trees were conducted simultaneously by personnel from the Maine Forest Service, and the USDA Forest Service, Durham, New Hampshire.  A total of 222 larch trees (Larix spp.) were found in the survey area in Brunswick; 11 were native tamarack (Larix laricina (Du Roi) K. Koch), and 211 were determined to be European larch (Larix decidua Mill.) or European larch hybrids, based on cone and bark characteristics. No other trees in the survey area are susceptible to the larch canker pathogen. 

A total of 32 larch trees were found to be infected.  All infected trees were on the golf course grounds proper, and all infected larches have been determined to be European larch.   Four of the eleven native tamarack occur on the grounds of the golf course; the others are widely scattered in the native woodlands and a small residential area between the golf course and Interstate 295.  None of the native tamarack was found to be infected.  All cankers observed on the infected trees were branch cankers.  There were no stem cankers. Six trees have but a single branch canker. As near as can be determined, there has been no mortality from larch canker, although a few heavily-infected trees had several dozen branch cankers

Eradication Plan:  Because so few trees are infected, because the infected trees were closely clustered in distribution, and because adjacent, susceptible individuals were few and widely scattered, it seemed appropriate to attempt an eradication of the infested trees. 

The eradication plan called for felling 26 of the 32 infected trees, and pruning infected braches from the six trees found with only single branch infections.  The branch and top material will be burned on-site (on the golf course grounds), prior to April, 2009.  The larger stem material was milled into dimension planks and landscape timbers, again to be used on the golf course grounds.   Slab material generated from the milling will also be burned on-site prior to April, 2009.  

Although the pathogen can survive as a saprophyte for some (unknown) period of time (USDA 1991), it has been shown to be quickly inhibited by competing microorganisms (Yde-Anderson 1979, Sinclair and Lyon 2005), and is not easily isolated from any wood  or bark tissues other than those of active canker margins.  Tree infection occurs via ascospores infecting wounds through the bark.  The development of new ascocarps has not been observed to occur on dead wood or bark. Additional precautions taken included sweeping and disinfesting all milling equipment before it left the site, to eliminate potential for spreading the pathogen or any infected material.

Tree felling and most of the slash burning work was completed by mid-December, 2008.  Burning any remaining slash, and burning the slab material generated from the milling process is scheduled for completion by April, 2009.   Property managers have been fully cooperative, and have requested the work to be done in the winter season in order to limit damage to the greens from harvesting equipment traffic.  This scheduling has also fit well with the disease survey progress. 

Future Monitoring:  Since all larch tree locations have been mapped, re-surveys will be conducted on at least an annual basis for the next five years, to quickly locate and remove any new infections (infected trees) that may occur, or others that may have been missed.  Particularly close monitoring will be conducted on those trees that receive only the pruning treatment for canker removal.

This incidence of larch canker appears to have developed from a separate introduction of the pathogen, and not from the spread of the pathogen from existing known locations already in quarantine.  Surveys of larch during 2007 and 2008 in neighboring towns, and in towns located between the Brunswick infestation and the current quarantine boundary have not revealed any other infestations.  Additional survey work also will be focused in these adjacent, un-infested towns during the next five years.

Ornamental European larch were likely introduced to this site and established for landscaping purposes, and may have been infected in the nursery.  Specific origin locations and tree establishment records are not available.  The oldest larches are approximately 80 years of age; the youngest are estimated to be about 35 years of age.  

Initial observations indicate that the disease has been at this location for at least fourteen years. European larch is also more resistant to the disease than is native tamarack, which may account for its slow spread and the lack of stem cankers. 

References

Sinclair, W.A., and H.H. Lyon. 2005.  Diseases of Trees and Shrubs.  Cornell University Press.  660 pp.

USDA. 1991.  Pest Risk Assessment of the Importation of Larch from Siberia and the Soviet Far East.  USDA Forest Service Misc. Pub. No. 1495.

Yde-Anderson, A. 1979. Lachnellula willkommii canker formation and the role of microflora: A literature review.  European Journal of Forest Pathology 9:6:347-355.