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Management of six-spotted mitein WA’s avocado orchardsBY ALISON MATHEWS RESEARCH SCIENTIST, DPIRD Western Australia’s growing avocado industry is being supported to confidently protect its orchards by managing the pest six-spotted mite (Eotetranychus sexmaculatus) through the provision of science, advice and protocols. A new three-year project, Management of six-spotted mite in WA avocado orchards — Phase 2, commenced late last year to identify and develop effective six-spotted mite management options for avocado orchards incorporating cultural, biological and chemical practices. It is building on the work of the previous six-spotted mite project that finished in 2019.
Knowledge gained from the current, six-spotted mite project will lead to the development of integrated pest management guidelines for the WA avocado industry intended to improve marketable yield, promote the uptake of established on-farm best practice, and help ensure increased competitiveness in the global marketplace.
The guidelines will include information on when and how to monitor for pest and predatory mites, and the role of both natural and mass reared predatory mites in six-spotted mite management. The relationship between tree health, mite numbers and leaf fall, and miticide application recommendations incorporating resistance management, the impact of chemical control on beneficial species, and the effect of timing and application method on control, will also be covered.
Avocado industry stakeholders will be advised of field walks and workshops to be held during the project.
Current and future activities
Monitoring of six-spotted mite in avocado orchards commenced in January 2020 and for the past six months, the project team has visited 12 trial orchards every fortnight to survey six-spotted mite, predatory mites and other beneficial insects.This surveillance program helps confirm seasonal trends, identify sites suitable for coming trials, and determine the impact of various management strategies on pest and predatory mite populations. Mite numbers are generally low in summer and winter, with the most rapid increase and highest numbers experienced in spring, when trees are under stress from holding near mature fruit and supporting new vegetative growth, flowers and newly setting fruit.
Spring is therefore the most critical time for mite monitoring and management, and leaf fall resulting from mite damage.
Planned activities for the first spring season of the project include:
Releasing mass reared predatory mites that are yet to be tested in a field situation and measuring their impact on pest mite numbers;
Applying prey/pollen treatments in an effort to increase the number of predatory mites already present in orchards and measuring their impact on pest mite numbers;
Monitoring of six-spotted mite in avocado orchards commenced in January 2020.HIGH numbers of six-spotted mite can lead to severe defoliation of avocado trees. SIX-SPOTTED mite are found on the lower leaf surface where they feed however, symptoms of feeding damage can be seen on both the upper and lower leaf surfaces.
Testing leaf nitrogen levels of trees with varied levels of defoliation to determine if there is a link and if nutrition can play a role in pest mite management; and
More intensive leaf sampling to determine the best monitoring strategy for growers that is reliable and easy to use.
Project partners Managed by DPIRD, with partners Biological Services, Queensland Museum, and the New Zealand Institute of Plant and Food Research, the project is funded by Hort Innovation with in-kind support.
The research will see DPIRD undertake on-farm monitoring, and field studies and trials across a number of orchards in the Manjimup/Pemberton area.
Staff from Biological Services and the New Zealand Institute of Plant and Food Research will assist with this work, bringing with them knowledge and experience in mite monitoring, the commercial use of predatory mites, management of six-spotted mite in avocados and development of integrated pest management programs.
The combined experience of monitoring from the preceding project, current practices employed by growers and local mite monitors, such as Biological Services, and overseas methods, with input from the New Zealand Institute for Plant and Food Research, will be reviewed for use in the development of a monitoring and sampling protocol.
A mite specialist from Queensland Museum, who is part of the project team, is tasked with identifying predatory mites collected from commercial orchards and confirming the species of pest mite in WA currently regarded as six-spotted mite through morphological and molecular data.
Confirmed identification of the local pest species will help in determining management options, particularly the use of predatory mites, as they can be species specific. Background Six-spotted mite is native to central America and was first recorded in WA in 1986 on avocado seedlings from eastern Australia. The pest has particularly affected avocado orchards located in the Pemberton / Manjimup area of the South West region, causing economically significant damage.
While present in eastern Australia, it is not considered a pest of avocado there. It is, however, a pest of avocado in New Zealand and California, United States.
Even low numbers of the mite in avocado orchards can lead to defoliation of trees, which has flow on impacts including exposure of fruit or sunburn and a subsequent downgrade in quality and price received, or earlier than scheduled picking of fruit to prevent sunburn. When many trees are defoliated and fruit is harvested, the result is a potential glut of fruit on the market instead of the preferred steady supply that meets grower needs and market demand. Avocado industry in Western Australia Growth in avocado production and a jump in prices in recent years underpinned a 780 per cent increase in the value of this sector in WA, which is now valued at about $200 million annually and represents about 40 per cent of WA’s total fruit crop by value. The volume of the avocado crop is now comparable with apple production, which is the State’s largest fruit crop by quantity. The bulk of the value in the avocado sector remains in the Australian domestic market, with export sales making up just 4 per cent of WA’s total overseas fruit sales value.