Tackling the destructive Red Legged Earth Mite
06 Sep 2022
PRODUCTION ADVICE & NRM NEWS - SEPTEMBER 2022 - AGRICULTURE & AGRONOMY
By Adrian Smith, Senior Land Services Officer - Mixed Farming Systems
P: 03 5881 9932 | M: 0447 778 515 | E: firstname.lastname@example.org
Red legged earth mites (RLEM) (Halotydeus destructor) are significant pests of grain crops and pastures across NSW.
Whilst autumn and winter are usually the times when we see significant damage from infestations, we can still see significant numbers and resulting damage as we move through spring.
Warm, not hot, and moist conditions, such as those many are experiencing this spring, are ideal for RLEM. In pastures, for example, where we are trying to maximise spring growth and seed set, RLEM activity can have serious impacts.
Ongoing monitoring, coupled with targeted action, will help keep numbers in check, minimise impacts on crops and pastures, and importantly help to reduce egg laying so, helping to reduce numbers next autumn.
What do RLEM look like?
The majority of producers will have seen RLEM in their paddocks. They are part of the mites (Acarina) family, which because of their extensive habitat and small visual size, can be difficult to identify.
Like other mites in the family, RLEM has a nymph and adult life cycle stage. They initially have 6 pinkish/orange shaded legs. They undergo three nymphal stages to reach adulthood and a full body length of 1 millimetre, which is oval-shaped and velvety black in colour. During the nymphal stages, they gain two more legs to have 8 distinctive red legs by maturity.
Figure 1: Red legged Earth Mites (RLEM) Source: A Weeks – CESAR, Umina, P, Agriculture VIC, 2017.
The most important distinguishing characteristic of RLEM is that they generally tend to feed in groups or clusters.
When looking for RLEM, look at the plant's leaves first, and if mites cannot be spotted, observe the soil surface as RLEMs will often be sheltering in leaf sheaths and under soil debris when conditions are warmer. Observing the same few plants or patches of ground for 10-15 seconds should be enough time to spot mites moving around if they are present.
What are the signs of damage?
Most damage to crops and pastures by RLEM occurs at the establishment, which reduces seedling development and long-term survival. Monitoring for RLEM should occur regularly in crops three weeks after emergence. However, in spring, pastures can also be susceptible, particularly legumes.
Heavy feeding damage can impact the seed set if RLEM threshold control levels are not kept to a minimum. RLEM affect a large variety of crops, including canola, cereals (wheat, barley, oats), lupins, faba beans, field peas, sunflowers, lucerne, vetch, some grasses and pasture legumes.
Many weed species, such as Capeweed and Paterson’s Curse, are hosts for RLEM.
The most noticeable features of RLEM in-crop damage are caused by their feeding and are seen as silvering or white discolouration of leaves. The “silvering” is often mistaken for frost damage. Where infestations are severe, plant leaf distortion, shrivelling, or death of young seedlings will also occur.
Figure 2: Typical leaf damage “silvering” caused by RLEM. Source: Micic, S. DPIRD2015.
The key is to get out in your paddocks and look. The best times to check for mites are in the mornings when mites are feeding on leaves and on overcast days. As the day warms up, the mites take shelter in the leaf sheaths of plants and in organic debris.
What are the control options?
There is a range of chemical, biological and management control options.
Chemicals are the most commonly used control option against earth mites. While several chemicals are registered for control of active RLEM in pastures and crops, there are no currently registered pesticides that are effective against RLEM eggs.
There is also increasing evidence of resistance to synthetic pyrethroid and organophosphate chemicals within Australia.
To help manage resistance issues, producers and their advisors should use thresholds to assist with decisions around control actions and types of chemicals, use seed dressings where populations are low to moderate, and rotate insecticides with different modes of action.
It is important to note some crops, including wheat and canola, have shown, under some circumstances, to have the ability to compensate for crop damage from RLEM. Therefore, working to thresholds becomes important before using an insecticide or miticide, and your choice of plant variety(s) is also important if you have a known paddock history of RLEM problems.
There are at least 19 predators and one pathogen known to attack RLEM, including beetles, other mites, earwigs and spiders.
Leaving shelterbelts or refuges between paddocks will help maintain natural enemy populations. Natural enemies residing in windbreaks and roadside vegetation have been demonstrated to suppress RLEM in adjacent pasture paddocks. When insecticides with residual activity are applied as border sprays to prevent mites from moving into a crop or pasture, beneficial insect numbers may be inadvertently reduced, thereby protecting RLEM populations.
Rotating crops or pastures with non-host crops can reduce mite colonisation, reproduction and survival. For example, before planting a susceptible crop like canola, a paddock could be sown to cereals or lentils to help reduce the risk of RLEM population build-up.
Clean fallowing and controlling weeds, particularly broadleaf weeds like capeweed, pre- and post-sowing, can also reduce mite numbers as they provide important breeding sites for RLEM. Use paddock history to determine the best species to sow.
Appropriate grazing management can reduce RLEM populations to below damaging thresholds. A shorter pasture with exposed soil will limit the growth of mite populations. This can be an effective strategy in late spring as it reduces the amount of RLEM producing over-summering diapause eggs, resulting in less RLEM hatching the following autumn.
Long-term control strategies
Knowing the lifecycle of the RLEM can help to exploit its weaknesses. This gives producers control options and time from careful monitoring for early intervention to minimise the mite damage.
A long-term control strategy is to use the Australian Wool Innovation (AWI) Timerite® system developed by CSIRO.
Timerite® is a tool that uses environmental data (primarily day length) to predict when diapause eggs are likely to be produced in spring – reducing the number of mites hatching next autumn
The tool provides a location-specific date for when spraying should occur (if necessary). This gives growers a window of opportunity to strategically target red legged earth mite-problem paddocks.
Optimum dates for red legged earth mite control in eastern Australia are mostly between mid-September to mid-October. Exact dates are available through the Timerite® model.
The date for spring spraying is unique to each property and remains constant from year to year. It is recommended that spraying be carried out within a two-week period before the optimal date.
Some examples of indicative dates are:
- Moulamein area - 11 September
- Deniliquin area – 16 September
- Corowa area – 26 September
- Holbrook area – 15 October
- Tumbarumba area – 19 October
As the dates outlined above are indicative only, it is recommended that producers access this website and enter the precise location of your paddock(s) (Latitudes and Longitudes) into the Timerite® calculator to determine the optimum spray date for you.
If you have any concerns, please speak to your local advisor, agronomist or the Agriculture team at Murray LLS. Alternatively, the GRDC has an excellent publication with which producers should familiarise themselves with managing RLEM.
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