Redlegged earth mite

The sudden drop in temperatures over the last 10 days has made mass hatchings extremely likely.

 

Predictions of egg hatch

A number of reports have been received of redlegged earth mites in moderate numbers in various crops and pastures in the Riverina and Central West Slopes & Plains district of NSW. In Victoria, young populations of mite nymphs have been observed in the Northeast (Albury, Wangaratta), the Wimmera (Horsham, Ararat), the Western district (Colac, Penshurst) and North Central (Kilmore).

We have again run the redlegged earth mite (Halotydeus destructor) egg hatch prediction model (see PestFacts Issue No. 1) for these regions. This model is currently under validation. In southern NSW, the notably cooler temperatures that have followed the wet conditions in late April are likely to be the trigger for mass egg hatches from about May 9th. This would mean damaging infestations are likely to become more apparent in crops from mid to late May. In central and southern Victoria, the model predicts peak egg hatch from about April 24th, suggesting damaging infestations will become apparent around the second week of May.

How does the model work?

The strategy that redlegged earth mites have evolved to survive between seasons is complex and clever. Essentially their challenge is to ‘heat proof’ the eggs over summer (diapause) as they sit exposed in the soil surface, and with the onset of autumn, to resist hatching until their food sources (annual plants) have germinated with a reasonable probability of establishment. To achieve this they employ two triggers: a minimum rainfall and a minimum temperature requirement. Recent research at The University of Melbourne suggests that the process of egg development in autumn requires at least 10mm of rain over a maximum of three consecutive days, followed by 10 days of average† daily temperatures remaining below 16°C. This minimises the risk that mite eggs will hatch (and perish) in early autumn following a false break. The research also suggests that these thresholds may differ in Western Australia.

† The concept of the average day temperature was devised by CSIRO Entomologist, Dr Murray Wallace, in the 1970’s. He calculated a ‘mean’ day temperature where the daily maximum is weighted over the daily minimum.

Click here further information about the redlegged earth mite, including control options.

 

* Sources of field reports of earth mites

Damien Barri – Grower (Central Victoria)

Allan Edis – Agronomist, Landmark (NSW Riverina)

Warwick Nightingale – Agronomist, Delta Ag (NSW Riverina)