South Perth, Western Australia
October 7, 2010
Canola growers are advised to monitor their crops for Diamondback moth (DBM) and aphids and consider treatment options in relation to the impact of the dry season.
The Department of Agriculture and Food has had unusually early reports of the pests, particularly in the Southern Agriculture Region, brought on by the dry finish to the season.
Entomologist Svetlana Micic said many crops were moisture stressed and some growers were considering making their canola crops into hay or silage.
Ms Micic said growers should consider their pest treatment options carefully, especially if their crops were drying off.
“There have been reports of high DBM numbers around Borden, Jerramungup and the South Stirlings,” she said.
“DBM can be patchy, so it is best to check crops using a sweep net in more than one section of the paddock for the pest.
“If lots of small caterpillars are visible then that mostly indicates the population is on the rise. If growers find more than 100 DBM larvae in 10 sweeps they should consider spraying if crops are at the mid to late flowering stage.”
Ms Micic warned there was increasing resistance of DBM to synthetic pyrethroids and alternative chemical controls can be more expensive.
Trials have shown that using higher water rates when applying sprays led to better penetration of the chemical into the crop canopy as 20 per cent or more of DBM larvae can be found on the lower leaves.
“This needs to be weighed up when you are considering control options especially in light of lower yield prospects with a poor rainfall outlook,” she said.
“It is a good idea to check the crop post spraying to see how effective the spray was. If numbers of DBM larvae remain high, a second spray is often required within seven days.
Low levels of canola aphids have also been widespread throughout the Southern Agriculture Region and are likely to increase as the warmer weather increases.
Ms Micic said control measures were advised if canola crops had 20 per cent or more of flowering spikes infested with aphids and if crops were moisture stressed.
“Growers should check more than one section of the crop for aphids and walk in at least 15m from the edge of the crops as aphids such as cabbage aphids tend to be found on the crop edge,” she said.
“Aphid numbers can crash dramatically due to parasitism or disease and it is worth checking to see if there is any parasitism on aphid populations. Parasitised aphids are bloated and shiny.”
Ms Micic said if growers were going to spray they should consider applying chemicals that were softer on beneficial insects.
For more information about the incidence of crop pests and control options visit the department’s weekly online PestFax e-newsletter www.agric.wa.gov.au/pestfax
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