Pestfacts Southeastern Key takeaways
- An early autumn break and recent cool temperatures mean redlegged earth mite (RLEM) diapause eggs are predicted to have hatched in some regions, including Ballarat and Hamilton.
- If your crops are establishing and growing rapidly close to egg-hatch in your region, RLEM may not pose a significant threat.
- Use the RLEM hatch timing tool regularly early in the season to find out when eggs are predicted to hatch in your region, help guide monitoring and inform whether control is warranted.
Few pests are as infamous across Australia’s southern grain belt as the redlegged earth mite (RLEM), Halotydeus destructor, a species whose very name literally means ‘one who destroys’.
The highest risk for winter-sown plants occurs when egg-hatch coincides with crop emergence and during early growth stages, particularly if ensuing RLEM numbers are high.
The timing of this egg-hatch depends on local climate conditions. This season, some regions have already reached that point. Find out when eggs are predicted to hatch in your locality using the RLEM hatch timing tool.
RLEM hatching in autumn
To understand why RLEM hatching is related to climate conditions, it pays to know a bit about their biology.
RLEM has a clever strategy for surviving the hot summer months. During winter and spring, females produce specialised eggs, called diapause eggs, that remain within their bodies after they die. The corpse of the mother protects the eggs, keeping them safe over summer.
These eggs hatch the following year in autumn once two factors are met: moisture and temperature. In southeastern cropping regions, this is 5 mm of rain over 5 days followed by 10 days of mean daily temperatures* below 16 °C.
Once hatched, RLEM nymphs will take 4–6 weeks to develop into mature adults and begin reproducing. That timing of the egg hatch matters because the greatest crop risk occurs when hatch overlaps with emergence or early growth. If populations are large enough during crop establishment, their feeding can lead to plant death.
How does this season compare to last?
Most cropping regions have likely met the moisture requirements for egg-hatch from rainfall events in March and April.
With the onset of cooler weather, temperature requirements have also been met in some regions. This includes Ballarat and Hamilton, where eggs were predicted to hatch around April 16–17.
This is considerably earlier than last year, when eggs took longer than usual to hatch, largely due to warmer-than-average temperatures during autumn. For example, in 2025, egg-hatch was expected around May 7 and 28 for Ballarat and Hamilton, respectively. That’s 3–6 weeks later than this year!
Check the hatch timing tool
The best way to judge your risk is to check the hatch timing tool for your region and compare it with crop stage.
If hatching is predicted soon and your crop is still at an early stage, risk of damage may be higher, particularly in paddocks with a history of RLEM.
If your crop is already established and growing strongly, RLEM may not pose as significant a threat.
Similarly, monitoring around predicted egg-hatch dates can show whether RLEM densities are too low to warrant control, avoiding unnecessary spray applications.
To find out predicted hatch dates in your region, access Cesar’s RLEM hatch timing tool. If your region is currently showing an ‘unhatched’ prediction, check again every 4–5 days.
Further help with RLEM
For further up-to-date management information, consult the RLEM Best Practice Management Guide.
If you experience a chemical control failure and want to get your RLEM samples tested for insecticide resistance, please contact:
Dr Aston Arthur, aarthur@cesaraustralia.com or
Ian Thomas, ithomas@cesaraustralia.com
*MDT=Tmax–(Tmax–Tmin)/4
Authors
This article was authored by Ian Thomas, Julia Severi and Lilia Jenkins from Cesar Australia.
Cover image: Photo by Andrew Weeks, Cesar Australia
