Recent applied research enhances our toolkit to manage redlegged earth mite
Where have they been reported?
Redlegged earth mites (Halotydeus destructor) are now widely active, particularly in high rainfall areas and irrigated paddocks. We have observed high populations in the Western district of Victoria. There have been a few reports of redlegged earth mite in the southern Riverina of NSW. They have also been reported from North East Victoria. It appears as if the mites are coming from a slow start.
Predictions of egg hatch
In PestFacts Issue No. 1 we predicted hatch dates for redlegged earth mites in many cropping regions. We have now run the model for regions where the mite had previously not been predicted to hatch. (The model predicts the date of peak egg hatch; damaging infestations will become visibly apparent about a week later).
- In the Victorian northern Mallee, significant egg hatch still awaits adequate rain. Some mites will have hatched, but probably not most.
- In the Victorian Wimmera and NSW Riverina (northern areas), peak egg hatch is expected on 20-21st May. There have been some mites reported in the Riverina, but an earlier peak hatch was unlikely because of relatively warm temperatures in early May.
As we seek to improve the performance of the model, we are keen to receive feedback on its accuracy. Please send your comments and feedback to email@example.com.
Knowing when to spray
Recent research conducted by The University of Melbourne has led to the development of preliminary economic thresholds for redlegged earth mites in canola. These thresholds are based on shade-house and field trials conducted over 3 years as part of a research project funded by the Grains Research & Development Corporation. The new thresholds should reduce many uneconomic sprays and save growers money. Spraying only when it is economically viable and avoiding unnecessary spraying will also reduce the risk of redlegged earth mites developing insecticide resistance.
It is important to note that the data underpinning these thresholds is still preliminary and needs further validation in the field. It is hoped that PestFacts subscribers will provide feedback over the coming months so the thresholds can be refined. Please send your comments and feedback to Paul Umina at firstname.lastname@example.org or phone 03 9349 4723.
Preliminary economic thresholds in canola:
At the cotyledon stage:
If visual mite feeding damage (silvering or whitening) to 20% of plants or more and the presence of mites, treatment is warranted. If not, recheck at the 1st true-leaf stage.
At the 1st true-leaf stage:
If there are 10 mites per plant, treatment is warranted.
If there are fewer numbers of mites don’t spray. Recheck paddock in 5 days if crop growth is slow, or in 10 days if crop growth is rapid.
At the 2nd true-leaf stage:
If there are fewer than 30 plants/m2 and the presence of mites, treatment is warranted.
If there are greater than 30 plants/m2 and the majority of plants show no visual mite feeding damage, don’t spray. Recheck paddock in 5 days if crop growth is slow, or in 10 days if crop growth is rapid.
Later plant development stages:
Once plants reach the 3rd true-leaf stage there is no benefit in spraying, except when plants are under severe stress (moisture stress or waterlogging) coupled with mite numbers greater than 2000/m2.
Sources of field reports of redlegged earth mites
Alistair Crawford – Development Manager, Adama (Victorian Northern Country)
Josh Douglas – Researcher, The University of Melbourne