. Hazard-rating systems in forest insect pest management : symposium proceedings, Athens, Georgia, July 31-August 1, 1980. Forest insects Biological control United States Congresses; Forest insects United States Analysis; Forest insects United States Management. system if many trees are involved. Then, too, we wonder if incipient root disease may not develop more rapidly when the host tree dies. That would introduce a bias relative to uninfested trees that con- tained similar incipient Figure for blasting to ex- cavate dirt from around roots to aid in examination f
. Hazard-rating systems in forest insect pest management : symposium proceedings, Athens, Georgia, July 31-August 1, 1980. Forest insects Biological control United States Congresses; Forest insects United States Analysis; Forest insects United States Management. system if many trees are involved. Then, too, we wonder if incipient root disease may not develop more rapidly when the host tree dies. That would introduce a bias relative to uninfested trees that con- tained similar incipient Figure for blasting to ex- cavate dirt from around roots to aid in examination for root rot infection. Nonetheless, some evidence of an as- sociation of root disease and suscepti- bility to DFB has been developed (Furniss et al. 1979b). In that exploratory study, four trees were selected from each of two infested groups. Each set of trees repre- sented the following conditions: suscep- tible (readily killed), intermediate (some larval mines present, but resinosis evi- dent), resistant (no larval mines, trees survived), and not attacked. Amount of root disease was generally correlated with success of DFB attack. Armillaria mellea (Vahl. ex Fr.) Quel was the most frequent- ly observed pathogen. Three trees with roots 70 to 90 percent killed were success- fully invaded by beetles. Two with 30 to 40 percent of their roots killed had most- ly unsuccessful attacks, and one tree with no visible diseased roots had no attacks. These trees were about 100 years old, grow- ing in a grand fir-pachistima habitat type and in well-developed, fertile soil. Onset of root disease in mature trees probably contributes to their suscepti- bility by increasing moisture stress (Vite and Rudinsky 1962), but we have examined too many infested DF that had no evident symptoms to believe that root disease is obligatory. Rather, we view susceptibil- ity as the product of complex relation- ships involving numerous factors, impor- tant among which is root disease. Injuries Fire Mainly bec
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