Effectiveness of routine forest surveillance in detecting pest and disease damage in eucalypt plantations

Abstract

Routine health surveillance of forestry plantations in Australia typically involves inspections from the air, roadside and ground to detect, identify and map health problems caused by pests and diseases. An often-cited objective of routine health surveillance is the early detection of new incursions of exotic pests and diseases. To be effective, this requires the incursion be detected when damage is often cryptic either because of low incidence or low severity. However, the reliability of routine surveillance in detecting damage when symptoms are still cryptic has not been tested. We measured the efficiency of aerial, roadside and ground inspections to detect nine different types of damage symptom ranging from very obvious (mortality and dead tops) to very cryptic (stem cankers and stem borers), each occurring at a range of incidences among five 3-year-old Eucalyptus globules Labill. plantations. Cryptic damage symptoms (stem borers, stem cankers and kino exudation) could not be reliably detected using any of the inspection platforms even when their incidence, within small patches, was as high as 2%. Conversely, dead tops were detected most efficiently by aerial inspection, at incidences as low as 0.1%. The crown symptoms produced by moderately severe insect defoliation or necrotic leaf lesions due to Mycosphaerella infection could be detected with equal efficiency from roadside and ground inspections but could not be reliably detected from aerial inspection. We conclude that the combination of aerial and roadside inspection provide sufficient resolution to detect operationally relevant damage, i.e. damage of sufficient severity to consider remedial treatment. The inclusion of ground surveys does little to enhance the capacity of routine health surveillance to detect the more cryptic damage symptoms that characterise the early stages of outbreaks by stem and branch-attacking pests and pathogens. Routine ground surveillance of plantations is unlikely to detect damage by new incursions at a sufficiently early stage when eradication may be feasible.