Grains Research and Development

Date: 15.09.2014

Diamondback moth alert for canola crops

Author: Rebecca Barr

While growers have been focused on the threat posed by green peach aphids, diamondback moth (DBM) also has the potential to cause significant losses in canola this season. Moths have been sighted in large numbers through South Australia across rainfall zones, and the September weather forecast could favour the moth’s development.

Diamondback Moth in Canola

DBM sighted by GRDC panel member Richard Konzag in his canola on August 28.

Photo: Richard Konzag

SARDI entomology leader Greg Baker has received numerous reports of DBM infestations.

“In most years in most canola cropping districts of South Australia, DBM is not common, it’s one of those pests that fortunately we don’t have to deal with very often. However this year, the green-bridge and above average temperatures in late autumn that favoured the green peach aphid were equally suitable for DBM to be present and colonising canola early,” he said.

“As we now come out of winter, having had dry weather for much of August and temperatures starting to climb, we’re now in circumstances that are again quite favourable for DBM. We’re starting to receive agronomist reports that DBM are easy to find in many canola crops from all around South Australia, and I expect there will also be reports in Victoria and southern NSW.”

Growers are advised to sweep for DBM, and follow threshold guidelines (Table 1) in planning a control strategy.

Table 1: DBM threshold guidelines by crop stage.

Crop stage

Moisture stress*

DBM larvae threshold

Pre-flowering

Y

30 per 10 sweeps

Pre-flowering

N

50 per 10 sweeps

Early to mid-flowering

N/A

50 per 10 sweeps

Mid to late-flowering

100 per 10 sweeps

Pod maturation

200 per 10 sweeps

* Moisture stressed crops are more susceptible to insect damage. A lower threshold may be used in extended dry periods.

Source: GRDC Fact Sheet

“We advise growers work within the threshold guidelines before considering action to address DBM populations.  Respond when needed rather than going in early, because DBM numbers can naturally decline from beneficial attack and disease. In fact we’re receiving reports from agronomists of DBM numbers in some crops doing just that in the past 2 weeks.  Also it is important to recognize that spraying when it’s not required unnecessarily increases the risk of resistance development,” Mr Baker said.

Resistance is a major concern in DBM treatment, with only three products registered – two new synthetics (Affirm® and Success® Neo) and the biological insecticide Bacillus thuringiensis (Bt).

“While trials in WA have shown that Bt products work reasonably well in moderate infestations, growers are not confident in their effectiveness in more severe infestations,” Mr Baker said.

“The two synthetic products are equally effective, though Success® Neo is significantly more expensive. This results in one chemistry, Affirm®, being predominantly used to treat DBM, which is compromising the long-term effectiveness of that one product.”

While research to identify new chemistries is currently underway (see ‘GRDC Projects’), this means that growers should be careful when applying Affirm®, and not spray unless it is definitely required.

DBM have been shown to be susceptible to many beneficial insects including a number of parasitic wasps, damsel bugs, ladybirds and hoverflies. Fungal infection can reduce DBM numbers, and forecasts for light rain and warm temperatures could potentially favour fungal activity. Growers should look for signs of parasitic or diseased pupae, which are usually on the underside of leaves and may appear white and brittle, and consider this when testing thresholds. For instance, if an infestation is just on the edge of the threshold but a lot of beneficial insects and parasitized pupae are observed, spraying may not be required.

GRDC Projects

The GRDC is funding a number of DBM projects in the Southern Region.

  • DBM Control and Insecticide Resistance Management (SARDI): Tracking resistance levels to various insecticides in populations across western and southern Australia and facilitating the registration of new chemistries.
  • Regional movement of DBM and colonisation of canola in southern Australia (University of Adelaide): PhD project to improve the understanding of movement of resistance types within a population to manage resistance, and learn more about timing and sources of colonisation to better predict which seasons will present a risk of DBM damage.
  • Options for Improved Insecticide Use and Canopy Penetration in Canola (University of WA): investigating spray coverage and canopy penetration in canola, including a trial to be run this spring in the southern region.
  • Attract and Kill Technology for Diamondback Moth (University of New England): investigating the potential of a product with a food attractant to draw the moths, with a toxicant which will provide a lethal dose of insecticide.

Learn more about GRDC's work to improve DBM control

More Information:

Greg Baker,
08 8303 9544,
greg.baker@sa.gov.au

GRDC Fact Sheet: Diamondback moth.

GRDC Project Code DAS00094, UA00146, UWA00165, UNE00016

Region South