NUMBERS of diamondback moth (DBM) caterpillars in the Esperance and eastern Wheatbelt areas have been increasing, especially in earliest sown canola crops, and larvae numbers are starting to appear.
At Grass Patch, South East Agronomy Research (SEAR) agronomist India Warren-Hicks found 40-50 DBM caterpillars in an early-flowering canola crop on average in 10 sweeps in sections of the paddock which had been waterlogged and/or plants were moisture stressed.
Whereas in a later sown canola crop only 10 kilometres away, which was at the cabbage stage, low levels of DBM caterpillars were found.
Interestingly the 10 canola focus crops in the Esperance shire being monitored by SEAR had no larvae detected in sweeps.
Agronomists have also reported to the PestFacts WA, run by the Department of Primary Industries and Regional Development (DPIRD) that canola crops at Hopetoun, Scaddan and Munglinup have low numbers of DBM caterpillars causing some shot hole damage.
DPIRD research scientist Christiaan Valentine found an average of 11 DBM per 10 sweeps in bolting/early flowering canola crop near Narembeen, which was up from five per 10 sweeps the previous fortnight.
Mr Valentine also found two per 10 sweeps in a canola crop at Mukinbudin, but it was difficult to assess on an icy morning.
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He said a high spike of DBM moths were detected in the pheromone trap and shot-hole damage was easily seen in the leaves, so further monitoring was warranted to see if the increase in moths results in an increase in larvae.
"The earliest sown canola crops can be more at risk of early DBM increase and canola plants are more vulnerable to caterpillar damage when they are stressed due to dry or very wet conditions, and closer to flowering," Mr Valentine said.
"DBM caterpillar activity should slow down in cold, wet weather conditions and then ramp up in spring but DPIRD's Seasonal Climate Outlook report for July 2022 is predicting above average daytime temperatures for the July to September period which encourages pest activity and reproduction.
"Growers and consultants are advised to monitor for DBM, especially from August onwards, by doing at least four lots of 10 sweeps with an insect net at various locations in each crop."
As part of a Grains Research and Development Corporation funded project on DBM surveillance, DPIRD staff along with grower groups are conducting widespread surveillance for DBM moths and larvae in 51 focus crops throughout the grainbelt during the season.
So far, the surveillance project has captured high numbers of moths in traps for some northern, eastern and Esperance areas but low numbers, or no, DBM larvae.
In some cases, minor feeding damage to leaves was visible.
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