Bark scoring problem grafts in five Douglas-fir seed orchards: a case history.

Abstract

A bark-scoring trial was carried out on 379 of 1,234 grafts in five western Oregon seed orchards. Ages of grafted trees in 1983 ranged from 5 to 16 years. Scoring was done in April, June, or August of the first and third years of the 4-year test. Cuts across the defective interface of the union were made every 3.1 to 4.3 cm with a small, gas-powered chain saw. Many trees showed improved vegetative vigor after treatment. Annual mortality in the five orchards averaged just 1.6 percent when all defective grafts were treated. Diameter growth of rootstocks was least in incompatible grafts and greatest in compatible grafts. Form class (scion diameter divided by stock diameter) increased slightly during the study. The greatest improvement in average compatibility occured in trees treated in April. Among the three orchards treated in April, the orchard with the youngest grafts responded to scoring treatments most favorably. Two different types of graft incompatibility were found: the inherent type with brownline around only part of the circumference. The induced type usually began in grafts with one-sided compatible unions. Wound tissue that formed in bark scores of the induced incompatible grafts was usually free of brownline, but brownline appeared in all wound tissue of bark scores of inherently incompatible grafts. All the inherently incompatible grafts and some of the induced incompatible grafts will require additional treatments every 2 or 3 years to maintain a live cambium at the union.