Electrical resistance in relation to crown dieback symptoms, infection and growth in Eucalyptus obliqua and E. globulus ssp. bicostata.  G. A. Kile, J. D. Kellas and R. G. Jarrett.  August 1983.  14 pp. (unpubl.)

SUMMARY

In Eucalyptus obliqua L'Hérit. (messmate stringybark) infected by Armillaria luteobubalina Watling & Kile (armillaria root rot) or affected by regrowth dieback (with secondary Armillaria infection) stem electrical resistance (ER), measured with a Shigometer, was correlated with degree of primary crown dieback, epicormic shoot development, crown volume and Armillaria infection respectively. Because of high tree-to-tree variation, electrical resistance measurements could only distinguish between trees of extreme disease-severity classes. Use of insulated electrodes did not improve the relationships.

Thirty-year-old E. obliqua and E. globulus ssp. bicostata (Maid. et al.) Kirk. (Gippsland blue gum) grouped into four or five A. luteobubalina infection classes showed no differences in level or pattern of electrical resistance over a 16 month period. During the same period girth increment was significantly different between infection classes for E. obliqua but not E. globulus ssp. bicostata. Armillaria did not affect ER in tissues in advance of mycelial infection, whether or not it was a primary or secondary pathogen. A comparison of electrical resistance in trees stressed by bark and sapwood girdling and 2,4,5-T application with that in trees killed by A. luteobubalina, suggests that A. luteobubalina kills trees by the physical destruction of the vascular system, the trees eventually dying from water stress.

Also published:

Kile, G.A., Kellas, J.D. and Jarrett, R.G. (1982)  Electrical resistance in relation to crown dieback symptoms, Armillaria infection and growth in Eucalyptus obliqua and E. globulus ssp. bicostata.  Aust. For. Res. 12: 139-49.