December 2000 | 2400 | 0024-2372-MTDC |
Keith Windell, Project Leader
Grafted seed orchards of Douglas-fir are often subject to tree losses caused by delayed graft incompatibility. When the stock and scion (the grafted branch) are incompatible, the stock and scion wall off the foreign cells with a separation zone of dead, suberized (corky) tissue. The separation zone is termed “brownline.” This response occurs along the entire interface in the bark cells of both the stock and scion. This type of graft failure is the product of the defense mechanisms of each tree. The same process enables trees to wall off invading insects and disease organisms or to cover physical wounds with an impervious or protective covering.
If a graft becomes incompatible several years after grafting, seed production will be lost and genetic variability will be decreased. A number of years will be required to replace the incompatible grafts. Improving the long-term survival and performance of established grafts is difficult.
Bark scoring is one cultural technique that has potential to reduce graft losses and improve tree vigor. Numerous vertical cuts are made across the defective union (figure 1). The primary objective of bark scoring is to improve the flow of water and nutrients (translocation) across the graft union. Bark scoring Douglas-fir grafts temporarily overcomes the incompatibility by physically removing a portion of the barrier of dead tissue separating the living stock and scion cambial cells. New cambia differentiate across the cuts in the newly formed callus tissue. (Donald Copes, PNW-RN-487, 1989).
Figure 1—This failed tree graft was
scored with a chain saw.
Small gasoline chain saws are sometimes used to make the small vertical cuts required in bark scoring. Some orchard managers feel that the chain saws are hard to guide with precision and tend to butcher the trees. Chain saws are also awkward to operate and tend to throw chain oil into the cut. A small battery-operated tool called the Woodzig (figure 2) was highly recommended by some managers. Unfortunately, it is no longer available.
Figure 2—The Woodzig was a handy bark-scoring tool.
It is no longer
available.
The Missoula Technology and Development Center (MTDC) was asked to identify or develop powered tools for safe, precise, and efficient bark scoring.
Project Approach—A bark-scoring tool needs to be relatively inexpensive. Many tools and attachments were considered and purchased. The tools were quickly tested at MTDC to see if they had any inherent safety risks, such as kickback. Special guards were fabricated and the tools were sent out for field evaluation.
The Forest Service, United States Department of Agriculture (USDA), has developed this information for the guidance of its employees, its contractors, and its cooperating Federal and State agencies, and is not responsible for the interpretation or use of this information by anyone except its own employees. The use of trade, firm, or corporation names in this document is for the information and convenience of the reader, and does not constitute an endorsement by the Department of any product or service to the exclusion of others that may be suitable. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.
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