Redlegged earth mite hatching and monitoring strategies

As we experience cooler and wetter days, it’s time to turn our attention to the redlegged earth mite (RLEM) (Halotydeus destructor). Understanding the likely hatch dates of their summer diapause eggs is important to effectively monitor and manage this pest, especially in high risk paddocks.

Our online hatch timing tool is your go to guide, using local climatic data to predict these hatch dates. It serves as a valuable indicator for when to ramp up crop monitoring.

While monitoring for mites can be challenging, we’ve got some practical tips to help when out in the field.

The significance of knowing hatch dates

The redlegged earth mite poses a significant threat to establishing winter crops and pastures, potentially leading to economic loss.

In south-eastern regions of Australia, redlegged earth mite eggs, which have been lying dormant in the soil over summer, hatch after substantial rainfall (>5mm) followed by mean day temperatures below 16°C for a period of 10 days (McDonald et al. 2015). In paddocks with a high risk or a history of heavy redlegged earth mite infestations, spraying might be required, and timing is crucial.

Optimal spray timing occurred in the previous spring with TIMERITE®, but control may also be warranted in autumn following the first hatching of the over-summering eggs (in April-May) to protect emerging crop plants.

Understanding when mites hatch can help you avoid unnecessary spray applications and can make the difference in protecting crops. Eggs are not affected by pesticides so spraying before mites have hatched will be ineffective. Similarly, if early sown crops are sufficiently large before mites hatch or if mite densities are low following hatching, RLEM may not pose a significant threat to crop damage.  

So don’t rush into spraying: remember to reach for the chemicals only if redlegged earth mite numbers exceed established thresholds to avoid the evolution of insecticide resistance and loss of beneficial species.

Further details on economic thresholds are provided below.

Forecasting redlegged earth mite hatch dates in your area

Our team has developed a hatch timing tool designed to enhance monitoring for redlegged earth mite pressure during crop emergence. The tool predicts the hatch dates of mite eggs in autumn for the current season.

CLICK HERE TO GET YOUR PREDICTION

By utilising real-time weather data from the current growing season and historical data from the past 25 years, it estimates the timing of egg hatch in a user-defined location. Meaning it’s a tailored prediction based on the unique conditions of your area.

Figure 1 shows the average predicted hatch dates for different regions in Australia, with each colour indicating the predicted month of hatch.

But let’s face it, there’s no such thing as an ‘average year’. Figure 2 illustrates the hatching predictions based on climatic data for the current year. Certain areas have already experienced conditions suitable for redlegged earth mite hatching, and if your region is one of the lucky ones, it’s time to prioritize monitoring accordingly.

Use the online hatch tool for more precise predictions in your region for the current season.

Figure 1. Predicted hatch date using averaged climatic data for the redlegged earth mite. Map by Cesar Australia
Figure 2. Predicted hatch status at 30th of April using climatic data for the 2024 season. Map by Cesar Australia.

Tips for effective monitoring 

Regular monitoring of redlegged earth mite numbers in susceptible crops, such as canola, provides insights into the risk of economic damage and the need for management.

Autumn monitoring is particularly important as large mite populations can overwhelm the protection offered by seed treatments.

Accurately monitoring mites can be challenging. Here are some tips for when you’re in the field:

  • Avoid sampling in sunny conditions; mites prefer cloudy days
  • Timing is everything: monitor for mites early morning, or late afternoon when mites are most active.
  • Mites are best detected feeding on the leaves, but if not observed on the plant material, inspect the soil for mites.
  • Visually estimate the number of mites in a 10×10 cm square (100cm2) and repeat the estimates 5-10 times across the paddock.
  • Look for mite feeding damage on plants characterized by silvering or white discolouration of leaves.

Economic thresholds

Economic thresholds for the redlegged earth mite vary across crops and should be used as a guide only. Remember to factor in crop-specific factors like water stress or disease when making decisions. It’s not a one-size-fits-all situation; it’s about tailoring your approach for maximum effectiveness.

Canola
Cotyledon stage: If mite feeding damage (silvering) affects 20%+ of plants and mites present treatment is warranted. 1 true leaf stage: >10 mites/plant treatment is warranted. 2 true leaf stage: If there are fewer than 30 plants/m² and the presence of mites, treatment is warranted.  If there are more than 30 plants/m² and most plants show no visual mite feeding damage, then do not spray. More than 3 true leaves: 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.
Wheat and Barley: 50 mites per 100 cm²
Pulses: 50 mites per 100 cm²
Establishing annual medic pastures: 20-30 mites per 100 cm²

For information on economic thresholds and monitoring, click here.

Additional resources

Redlegged earth mite best management practice guide – GRDC

Crop and pasture mite identification video – Cesar Australia

McDonald G, Umina P, Macfadyen S, Mangano P, Hoffmann A (2015). Predicting the timing of first generation egg hatch for the pest redlegged earth mite Halotydeus destructor (Tucker) (Acarina: Penthaleidae). Experimental and Applied Acarology 65, 259-276.

Acknowledgements

Thanks to Paul Umina and James Maino for reviewing this article.

This web tool was developed by Dr James Maino through a GRDC investment (CES2010-001RXT) with contributions from CSIRO, Cesar Australia, the University of Melbourne, and the Department of Primary Industries and Regional Development.

Cover image: Photo by Andrew Weeks, Cesar Australia

What is Pestfacts south-eastern?

PestFacts south-eastern keeps growers and advisers informed about invertebrate pests and beneficials in broadacre crops and pastures during the winter-cropping season in Victoria and southern New South Wales.

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Since 2019 PestFacts south-eastern has been running through IPMforGrains: Best Practice Insect Pest Management, a project delivered by the National Pest Information Network (Cesar Australia, DPIRD, QDAF, NSW DPI, and SARDI). This project aims to provide grain growers and advisors with information on invertebrate grain pest occurrence and equip industry with the knowledge needed to implement integrated pest management practices. This initiative is a GRDC investment and includes in-kind contributions from all project partner organisations.

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