Eucalyptus pests and diseases, an overview
The Symphyomyrtus group of eucalyptus has emerged as the most suitable for plantation forestry in most parts of the world, characterised by site adaptability, fast growth and good form along with suitable wood properties. In New Zealand, species within this group (The southern blue gums such as E. globulus, E. nitens and E. macarthurii, eastern blue gums such as E. saligna and E. botryoides, the red gums including E. camaldulensis and E. teretecornis) were historically planted widely....and then the pests started arriving...and kept arriving, and will no doubt continue to arrive with Australia just across the ditch. These species are generally becoming harder and harder to grow successfully in New Zealand.
The Monocalyptus group of eucalypts, in contrast, remains relatively free of serious pest problems even today. This group includes the stringybarks (including E. muelleriana, E.globoidea, E.eugenioides, E. agglomerata and E. laevopinea) blackbutt E. pilularis, and the Ash group (including E. regnans, E. delegatensis, E. obliqua and E. fastigata). However they are not generally as tolerant of poor soil conditions caused by excessive drought and high water tables, and can be susceptible to leaf-disease, so do need some care in siting.
The balance of nature
Because Eucalyptus has been a minor component of plantation forestry in New Zealand, sufficient resources have not been available to counter pest introductions with natural enemies. This has led to an imbalance where pests are much more damaging than they are in their natural environment in Australia where they are controlled by predators and parasites.
However, Eucalyptus is the only fast grown plantation hardwood which could fill the $300 million demand per annum in New Zealand. Addressing the perceived risk to an emerging industry would require central government committment towards sustainable forestry with biological control over and above the piecemeal and underfunded efforts to date.