DBM moth mystery

30 Apr, 2003 10:00 PM
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THE absence of diamond back moth last year was an unexpected bonus for WA canola growers, but it means entomologists are no closer to solving the mystery of the pest.

DBM decimated canola crops in northern and central WA in 2001 but there was little evidence of the pest last year.

Perhaps the small and fragile moth headed east.

The 2002 season was the first time that eastern states growers have been affected by DBM, with outbreaks in NSW, Victoria and South Australia.

Agriculture Department senior entomologist Kevin Walden said GRDC and Agriculture Department trials focusing on control of DBM will continue in 2003.

"DBM has been present in canola crops for years but in low numbers causing no measurable damage.

"It may have come from a horticultural crop, be breeding somewhere in the wheatbelt or perhaps it migrates large distances under favourable conditions, aided by tropical rains," Mr Walden said.

"We are none the wiser following last season."

Because pesticide applications are not 100pc effective and DBM has no resting phase, the resulting overlapping generations require persistent use of chemical.

"It is difficult to time sprays because a proportion of all life stages survive the pesticide application," Mr Walden said.

"Growers are not getting total control but two to three sprays cost $50/ha."

The DBM life cycle is usually about four weeks but temperate dependent.

Ongoing research in 2003 will look at control measures such as the insecticide used, frequency of use and the method of application (spray volumes).

"The other aspect of research will be to establish population dynamics in the paddock and at a regional level, the idea being to work out where DBM is coming from and to give us some early warning signs," Mr said.

He pointed out that it had taken several years of data to establish the population dynamics associated with plague locusts and heliothis.

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