Canola: Diamondback moth strategy high on agenda

Coming to grips with the Diamondback moth.

WITH SOME growers losing up to 70 per cent of their canola crops over the past two seasons due to Diamondback moth (DBM), many have lost confidence in canola as a crop that can return a profit margin comparable to other options.

In response to growers' concerns, an extensive survey is being conducted to identify DBM's first flight into the region to predict outbreaks, according to WA Department of Agriculture Research Officer in Geraldton, Kevin Walden.

"If we continue to look at more efficient and effective pest and crop monitoring techniques and DBM population dynamics, we can develop a regional management package to ensure the economic management of the pest."

A management strategy would also include an assessment of the efficacy of a range of insecticides and methods of application that would maximise DBM larval mortality.

Speaking at the WA Agribusiness Crop Updates 2002, Mr Walden outlined the extent of DBM damage in WA and globally. He said while the Northern Agricultural Region (NAR) bore the brunt of the DBM crisis in 2000 and 2001, growers in central and southern areas also suffered, with significant yield reductions and poor grain quality.

"Across the world, Diamondback moth is considered the major insect pest of many commercially produced cruciferous plants, including canola," he said. Last estimates (10 years ago) of the annual cost of managing DBM were said to be more than $2 billion worldwide.

Existing DBM management strategies include regular crop monitoring with sweep nets for early detection and looking at the relative proportion of large to small grubs. If numbers reach the threshold of 200 in 10 sweeps, spraying is required.

"It's very important to monitor crops after spraying, as pest numbers can increase quite dramatically," Mr Walden noted.

Spray or rain — both good

Spraying can reduce numbers to less than 10 per cent, but they can return to the same level in two weeks.

If substantial rain is forecast, spraying should be delayed, as heavy falls can reduce DBM numbers by up to 90 per cent. Rain, wind and cold conditions limit population growth, as females are unable to lay eggs.

DBM concerns were raised at a Crop Updates discussion session, with the issue of predicting outbreaks high on the agenda. Many growers are wary of seeding canola, particularly in the NAR, and plantings are likely to be down 30-40 per cent this season.

Because canola crops have taken off in WA only in the last decade, there are still many unknown facts about DBM, making prediction of outbreaks difficult.

"The NAR hasn't grown canola for very long, so we hope this isn't the beginning of a trend. We have no idea where they come from, but we're trying to find the source," Mr Walden said.

Synthetic pyrethroid insecticides, currently being used, are not killing all larvae and growers often need to spray more than once.

"There are a number of DBM insecticides used in horticulture and, although quite expensive, they need to be assessed to see how well they might work in broadacre areas.

"It would take about five years of ongoing research to better understand and effectively manage DBM," Mr Walden said.

Contact: Mr Kevin Walden 08 9956 8555