In the first year of the project, field activities have concentrated on gathering information on the types of pests and diseases in orchards with some information on thier abundance and pest status.
While we have concentrated more on insect and allied pests of trees and truffles in the first year, some attention was given to identifying the causes of poor tree vigour and adverse symptoms on trees in orchards where growers have requested assistance. This has involved both oaks and hazelnuts trees.
Trying to identify causes of apparent tree diseases is far from straight forward. The possibility that even if the symptoms were initially the results of a primary disease, the presence of such a disease may be masked because over time secondary disease organisms become the dominant agent present. Alternatively, symptoms present may be related to stress through other than optimal moisture or nutrient levels in the soil.
One other factor related to variability in tree vigour of both oak and hazelnut trees is that trees are sourced from seed that is not true to type. By the very nature of the process to inoculate truffle host trees by collecting seed, the resultant trees will be quite variable genetically. This is often reflected in the range of tree vigour during tree establishment and so is not at all necessarily related to the presence of a primary disease agent. So far even for trees with some apparent symptom that could be considered a disease has yet to be conclusively associated with a primary disease agent that might otherwise be the subject of a management program to improve tree uniformity and vigour.
One problem where some type of dieback occurs in hazelnut trees appears to be best managed by allowing trees to consist of many stems.
Fauna in truffle orchards and truffle pests
A list of key pests has been developed based on field monitoring in WA orchards by project officers and information from growers, both through the survey and a recent trip to eastern Australia undertaken by Stewart Learmonth.
In Western Australia, tile traps and pitfall traps have been deployed in seven truffle orchards located at Bridgetown, Cowaramup, Manjimup, Pemberton, Northcliffe and Denmark. Two types of traps were used - tile traps to monitor fauna seeking shelter during the day such as molluscs, earwigs and slaters and pitfall traps to capture more mobile fauna such as beetles. During truffle season, pieces of truffle were placed in half the pitfall traps at each site to determine whether truffle feeders might be monitored more efficiently.
In terms of numbers, slaters and millipedes were the most abundant fauna recorded. Slugs had been thought to be a major pest from previous reports and this was confirmed by assessment of damage to truffles. However, the traps did not appear to be efficient in monitoring them. Although slaters were recorded in large numbers in one truffle producing orchard, there was no evidence that they were feeding on truffles. There was some evidence that millipedes were attacking truffles but further studies are required to clarify and confirm their pest status.
Also during truffle season on a fortnightly basis, we examined 50 truffles in each of the truffle producing orchards where traps were deployed to record fauna attacking truffles and the extent of damage to truffles.
The most significant discovery of the project to date was the damage caused by a beetle to truffles in the Northcliffe area of WA. We believe it is a native truffle beetle probably feeding on native truffles that may occur in the forests of south west WA. The beetle is about 3 mm long and 1.5 mm wide. It is black and tan and has clubbed antennae. The larval stage is white with a brown head and has three pairs of short almost unseen legs on the thorax. It is thought both larvae and adults feed on the truffle gleba resulting in a honeycomb effect which may render a truffle almost unsaleable.
Further studies are planned to clarify the distribution and biology of the “western truffle beetle” and to investigate management strategies to protect truffles.
In the second year of the project, we will be extending studies to the eastern states. Monitoring and in some cases demonstration studies of management techniques will be undertaken in orchards in New South Wales, Victoria and Tasmania visited by Stewart Learmonth in July/August 2016.
In WA, monitoring will continue in some orchards, but the emphasis of field studies will be on conducting demonstration studies related to improving management of some of the key pests, chiefly slugs and the truffle beetle.