Pests and Diseases
Leaf beetle eggs hatch around mid to late November and feeding larvae can cause severe defoliation through until late December at which time they fall from the tree to pupate.
Pest species have the capacity to rapidly increase in abundance and cause severe damage to forest communities and/or affect land use activities on neighbouring properties. This can reduce the commercial value of products that are grown to be harvested, and can diminish the intrinsic value of natural assets.
The term ‘pest’ is used as an umbrella term for any mammal, insect, plant, fungal, and microbial species that can cause damage that adversely affects natural and utilitarian values. There are two main categories of pests: exotic and native.
Exotic pest species are a particular concern because they establish without the suite of natural enemies that keep their populations in check. Native hosts may not have evolved the defences to resist or avoid the pest. For the most damaging exotic pest species the main approach is to limit their spread, particularly into the most vulnerable areas. Regulatory controls may be imposed to contain the spread of some exotic pests such as weeds.
Native pest species usually have a suite of natural enemies that regulate their populations, which means that damaging outbreaks are infrequent.
Management of native pest species in native forests aims to maintain this balance by using locally adapted seed for regeneration and avoiding conditions such as damaged standing trees, which may artificially enhance conditions for the pest.
A small number of native pest species also have the potential to regularly cause severe damage in plantations, which if not managed would threaten the viability of the plantation. For these pest species, management involves carefully selecting plantation species and genotypes to avoid enhancing susceptibility to the pest, maintaining habitat in the surrounding landscape to support natural enemies, using fertiliser to accelerate the establishment of seedlings, and maintaining the vigour of the plantation by timely thinning. If these actions are insufficient, monitoring to detect damaging pest populations is undertaken so decisions can be made on the need for additional management to reduce pest populations.
Forestry Tasmania’s pest management aims to:
- minimise the risk of new exotic pests from becoming established
- limit the area of PTPZ land that is adversely affected by exotic pests
- intervene to protect PTPZ land from severe impacts by pests, where appropriate and feasible
- assist the recovery of areas that have been adversely affected by pests
- minimise the need to use chemicals, and, where chemicals are used, use those that are effective and present a low environmental risk
Leaf beetles are the primary cause of the development of chronically thin crowns in eucalypt plantations in certain areas of the state. Such chronic defoliation has a major impact on performance with measured growth reductions of up to 90%.
Insect pests can cause serious damage in eucalypt plantations. Wherever possible, we prefer to monitor insect pests and rely on natural predators to control populations. However, chemical control is sometimes needed when significant outbreaks occur.
Currently, we use alpha-cypermethrin as part of our leaf beetle management. This chemical is a synthetic pyrethroid, similar to organic pyrethrum. It is approved for use under the Australian Forestry Standard, but not by the Forest Stewardship Council®. We are seeking permission from FSC® to continue our limited use of alpha-cypermethrin.
Image above: Leaf beetles of the genus Paropsisterna are a major defoliating pest in eucalypt plantations.
For more information, see Fact Sheet No.8 - Chemical use in forestry