Across the cropping and pastoral regions of Victoria and New South Wales, some areas are reporting a significant uptick in redlegged earth mite and blue oat mite activity; these mites can be major pests and can cause losses if not managed properly.
What’s the situation?
It’s not unusual to see increased mite populations this time of the year, during the cool, wet months from autumn to late spring. As crops move beyond the establishment phase and seed treatment efficacy diminishes, these mites often become more abundant. However, control is not always necessary.
The key concern is determining whether mite populations have reached levels that require intervention, and if so, understanding the key differences between each mite species to effectively manage their impact.
Spotting the difference: Identifying redlegged earth mites and blue oat mites
Redlegged earth mites (RLEM) and blue oat mites (BOM) are often mistaken for one another due to their similar appearance and the fact that they’re both active around the same time of year.
With a good eye you can tell the species apart in the field, although this can be challenging due to their small size. Some key differences in distribution and host plant preferences can also help you identify the most likely suspect.
- Blue oat mites: BOM have a blue-black body with a distinctive red mark on their back. They are usually found singularly or in very small groups.
- Redlegged earth mites: RLEM have jet-black bodies and lack the red marking. They are usually found in larger groups than BOM. Additionally, RLEM are typically not found further north than Dubbo, NSW.
While both species are often found together in mixed populations, RLEM are generally more prevalent. However, the relatively wet conditions over the past few years have favoured BOM populations, meaning you’re likely to find larger numbers of these in the field than usual.
Control considerations
Resistance to synthetic pyrethroids (SPs) and organophosphates (OPs) has been detected in RLEM populations across parts of Western Australia and South Australia. More recently, OP resistance has been detected in a number of RLEM populations in parts of Victoria, including in the Wimmera and North Central regions.
Currently, BOM have no known insecticide resistances. However, managing BOM is somewhat complicated by the presence of at least three species with varying tolerance levels: Penthaleus major, Penthaleus falcatus, and Penthaleus tectus.
P. major is the most common in eastern Australia, found across South Australia, Victoria, NSW, and Tasmania. It primarily feeds on pasture grasses, cereals, and pulses. Along with P. tectus, it has a lower tolerance to pesticides and is more easily controlled.
P. falcatus, which predominantly prefers canola and broad-leafed weeds, has a significantly higher tolerance to SPs and OPs than other BOM species.
Our Advice
- Monitor
Keep a close eye on emerging crops and pastures, especially those sown later in the season, for mite activity. Monitor susceptible pastures and broad-acre crops from autumn to spring for signs of damage and the presence of mites. Typical damage includes ‘silvering’ or ‘whitening’ of foliage, with severe infestations causing distortion or shrivelling.
Mites are easiest to spot feeding on leaves in the morning or on overcast days. If not seen on plants, remember to check the soil.
- Identify
If significant damage is noted, determine the species before deciding on the most appropriate management option.
See the blue oat mite and the redlegged earth mite PestNotes for further information on identification.
- Strategic chemical control
Economic thresholds for RLEM differ by crop, and crops can often recover from RLEM damage. Using the correct economic thresholds before applying insecticides ensures treatments are applied only when necessary. For detailed guidelines and further information, visit the Cesar Australia RLEM PestNote
You can use the economic thresholds established for RLEM in canola as a reasonable guide for BOM.
If BOM are detected and chemical control is necessary, ensure that insecticide sprays are applied at the full registered rate. This is particularly important for emerging canola crops.
- Resistance Management
If spraying is required, growers and advisers should follow good resistance management practices, including the rotation of insecticides, to minimise further resistance development.
Additionally, a simple in-field test has been developed to detect pyrethroid resistance in RLEM populations. Whilst synthetic pyrethroid resistance hasn’t been detected in Victoria yet, ongoing monitoring can catch emerging issues, allowing for adjusted pest management strategies.
- Minimize broad-spectrum sprays
Natural enemies, such as French Anystis mites, snout mites, small predatory beetles, and spiders, can help control mite populations. You can support these beneficial predators by using more selective insecticides – refer to the beneficials chemical toxicity table for guidance.
- Reach out
For any help with identification or control strategies, the Cesar Australia PestFacts team is just a call away. You can also visit the Cesar Australia website for a wealth of resources to help you manage mite pests.
Acknowledgements
Thanks to Paul Umina for reviewing this article.
Cover image: Photo by Andrew Weeks, Cesar Australia
