Home > Farm BioSecurity urging growers to keep watch for Avocado thrips

Farm BioSecurity urging growers to keep watch for Avocado thrips

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article image The Avocado thrip, Scirtothrips perseae, is 2mm long

Farm BioSecurity  have asked Australian avocado growers to keep a close lookout for a foreign strain of thrips, which could cause significant production losses if they were to arrive in the country.
Native to Mexico and Guatemala, Scirtothrips perseae was discovered damaging avocado fruit and leaves in the US state of California in 1996. Avocado thrips were presumably introduced inadvertently into California, most likely on young seedlings, and they now infest about 95% of the farms in that US state.  These thrips build to high densities on immature avocado foliage and fruit in late winter and spring, particularly in the southern regions of the state.

Despite this surge occurring during a time of worldwide avocado fruit trade, Avocado thrips have not yet been dispersed more widely. For numbers to build up, the Avocado thrips appear to be fully dependent on the young growing tissues of the Avocado tree.

The Avocado industry in Australia is currently on the front foot in managing the risks posed by exotic pests, however for Antony Allen, the Chief Executive Officer of Avocados Australia, keeping an infestation of Avocado thrips out of Australia is still a high priority.

"The introduction of a pest like this would be a disaster to the Australian industry. The feeding by adults and larvae causes serious distortion to young leaves, as well as extensive ‘corky' damage to the surface of young avocado fruit," says Allen.

Further to this damage to the fruit, the cumulative feeding damage by larvae and adults can also induce premature tree defoliation.

This brown scarring and damaged fruit means they are either unmarketable or get downgraded in packing sheds.

It is expected that an outbreak of Avocado thrips would have a substantial impact on affected growers both through production losses and reduced fruit quality. There is also no guarantee that the Avocado thrips could be eradicated once established.

To have to mount a response to Avocado thrips would cost industry and the community a great deal, and ongoing control costs would be significant.

The best approach to dealing with a threat of Avocado thrips will be to:

  • take every precaution when introducing new plant material onto orchards
  • maintain a lookout for Avocado thrips and any of the telltale signs of its presence on trees
  • report any discoveries and suspicions immediately to the Exotic Plant Pest Hotline on 1800 084 881.
Biological control of Avocado thrips has been attempted. However, the rate of breeding of this pest usually outstrips that of any predators and traditional biological control is not considered a viable option in commercial orchards.

Since 2007 there has been a national Avocado Industry Biosecurity Plan in place. This plan is currently being reviewed and updated with Plant Health Australia, and an Avocado Orchard Biosecurity Manual is set to be released in 2011.

"Maintenance of our plant health status is vital for retaining existing trade, negotiating access to new overseas markets and ensuring the future profitability and sustainability of the Australian avocado industry," says Allen.

Spotting Avocado thrips can be difficult. Due to its small body size (scarcely 2 mm long) and the undistinguished yellow colour, satisfactory recognition of an adult as a member of the genus Scirtothrips really needs expert examination under a microscope. For this reason rapid referral to an expert is recommended.

Farm BioSecurity can assist with more information on biosecurity and a range of pest control tools to help secure farms, and a future for the Avocado fruit in Australia.

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