Defoliation of Eucalyptus nitens on the Errinundra Plateau, Orbost District. I. First progress report.  F.G. Neumann, F.Y. Kassaby and R.J. McKimm.  July 1975.  17 pp. (unpubl.)

SUMMARY

Overmature good-quality stands of Eucalyptus nitens Maiden, as well as saplings along road-sides, were defoliated on the Errinundra Plateau in Orbost District during spring 1974. This report summarises the state of knowledge on the problem as at January 17, 1975, and describes research to be undertaken in 1975.

The disorder was distributed over 3,039 ha of forest, of which about 1,275 ha was severely defoliated, 591 ha moderately defoliated and 1,174 ha lightly defoliated.

Several species of native fungi, from at least 4 genera, have been identified on leaf and twig material. Among these, Aulographina (Thyrinula) eucalypti (Cke. and Thiess) v. Arx and Muller, was the most common, and has been found on leaf blades, petioles and the bark of branchlets. Damage to petioles and branchlets was very serious, as it can lead to premature leaf shed. The frequency of isolation of A. (T.) eucalypti indicates that this fungus is likely to be the principal causal agent. However, until A. eucalypti and the other fungi are cultured, and E. nitens plants are infected and develop damage similar to that observed in the field, there is doubt about the actual number of species which are involved in disease expression. Insects that were identified on leaf material do not play a significant role in the damage.

An aerial application of Copper hydroxide (0.9 kg a.i. Cu in 18.2 l water/ha) was made to part of the affected area on December 23, 1974 to determine possible control effectiveness and likely technical and environmental difficulties. It is too early yet to assess the effect of this treatment. As only 15% of emitted copper reached ground-located targets, it is evident that improved precision and application techniques will be required to avoid possible environmental damage.

Tree mortality is not expected to follow a single outbreak of the disorder, and it is unlikely that new leaf growth will be damaged severely in the spring of 1975.