Low-level field activity of DBM is a sign that it’s never too early to monitor.
Where have they been reported?
A sighting of caterpillars, resembling diamondback moth (DBM) larvae (green larvae, tapered at both ends), in the Victorian Wimmera provides an early reminder of the need to monitor brassica crops for this pest.
Sightings of DBM in winter 2014 were much more common than they have been this year.
SARDI researcher, Kym Perry, has reported that overall DBM populations in 2015 season stand in contrast to 2014.
In early autumn 2014, well before canola emergence, DBM populations were widespread on wild brassica hosts in South Australia. DBM went on to become a major pest of canola in spring 2014, although as yet there is no direct evidence to link early season occurrence with subsequent outbreaks.
In 2015, sampling in late summer revealed substantially lower larval populations on wild brassica hosts.
A pheromone trapping network currently operating in canola crops in South Australia have shown an increase in moth activity during June and July, which is likely to lead to low level egg laying and larval hatch this winter.
Kym’s research is investigating the processes of canola colonisation to aid the future development of forecasting and integrated management tactics for DBM. To assist with this research, Kym would appreciate hearing about sightings of DBM larval populations in canola this season (contact firstname.lastname@example.org, 0421 788 357).
About diamondback moth
Diamondback moth (Plutella xylostella) caterpillars are typically most abundant during spring and summer where they can cause extensive damage to canola foliage and seed.
As temperatures warm from late August, the pace of larval development and population growth increases considerably. At 28°C the DBM lifecycle takes only 14 days whereas at 12°C the lifecycle takes more than 100 days.
Accordingly, the current rate of development of DBM will be very slow due to the cool and frosty conditions. DBM build-up will also be limited by various beneficial species along with Zoopthora fungal infections (where wet weather conditions persist).
For the July to early August period, there is no imminent threat to crops.
However, we recommend monitoring for DBM larvae in canola crops at and beyond the rosette stage, particularly those sown in the vicinity of volunteer canola and weed brassicas.
Infested crops should be regularly monitored, particularly once conditions become relatively dry or warm.
Spraying at this time of the year is unlikely to be warranted.
At this stage, it appears unlikely that the 2015 season will experience the same degree of DBM activity as 2014.
Sources of field reports of diamondback moth
Kym Perry – Researcher, SARDI (South Australia)