It is important to correctly identify mites as they can be mitey confusing
- South Stirlings
DPIRD staff carrying out redlegged earth mite (RLEM) surveillance have found RLEM adults and nymphs in pastures at Manypeaks, suggesting that hatching has occurred. They also found Bryobia mites (adults and immatures) causing damage in a moisture stressed canola crop at the cotyledon growth stage at South Stirlings. There were no RLEM present. The canola crop is going to be sprayed.
Research scientist Emma Pearse (DPIRD) has reported finding balaustium mites on volunteer barley near Scaddan.
A mixture of warm weather and rainfall across the wheatbelt may prompt a variety of mites to emerge, coinciding with crop emergence.
Earth mites are tiny sap sucking pests of crops and pastures. High numbers of mites coinciding with germination is the worst case scenario because the tiny mites feed on and kill the tiny seedlings, even before the cotyledons have a chance to push through the soil properly.
Correct identification of mites is critical for effective control, as different species can vary in their susceptibility to certain insecticide groups, either naturally or through insecticide resistance. Chemicals applied for control of the wrong pest may result in expensive loss of plant seedling density or having to re-sow some paddocks.
Identifying different earth mites
The adult balaustium mite has a brownish / red body, red legs and looks similar in appearance to the redlegged earth mite. If viewed under a magnifying glass or microscope short, stout, velvety hairs can be seen covering the body. The adult balaustium mite grows to almost twice the size of redlegged earth mites. Several generations can occur each year.
Feeding by these mites cause distortion to cotyledons and a silver or white discolouration on leaves. Damage is more severe when seedlings are stressed (for example, cold, waterlogged or very dry conditions). For more information refer to the DPIRD Diagnosing balaustium mite page.
Redlegged earth mite (RLEM) adults are 1mm long with a black body and eight red-orange legs. RLEM have a cold temperature requirement (generally seven days below 20°C average daytime temperatures) before the eggs are triggered to hatch. Immature nymphal RLEM are often a more reddish colour than when they are mature. RLEMs do co-exist with blue oat mites so be careful not to incorrectly diagnose the two mites. For more information refer to the DPIRD Diagnosing redlegged earth mite page.
Blue oat mites look similar to RLEM (i.e. adults are 1mm long with eight red-orange legs and have a dark purplish-blue body) but they have a pale to red dot on their back. For more information refer to DPIRD’s Diagnosing blue oat mites page.
Adult bryobia mites are reddish-grey with a pie-shaped body, red legs and two long forelegs. For more information refer to DPIRD’s Diagnosing bryobia mite page.
Bryobia mites and balaustium mites are more likely to be seen feeding on plants during warm and sunny parts of the day whilst RLEM and blue oat mites will be more noticeable feeding on leaves on overcast cool days or early morning / late afternoon.
You can confirm the identity of mites by using the DPIRD MyPestGuide Crops app which includes images and information of mite pests. Alternatively, you can send images for confirmation through the PestFax Reporter app.
Before spraying mites it is important to know that economic damage generally only occurs if mites are present in very high numbers or if the crop is moisture stressed. In many years, and under good growing conditions, mites emerge from eggs during or after crop germination and the plants outgrow mite feeding damage. For more information refer to DPIRD’s Earth mites - economic considerations for management page.
For registered insecticide recommendations for mites refer to DPIRD’s 2020 Autumn/Winter Insecticide Guide.
Balaustium mites are notorious for being tolerant to a variety of insecticides and are often found in crops after they are sprayed with insecticides at rates which do not kill them.
Growers and consultants are urged to apply integrated pest management (IPM) strategies when managing RLEM due to cases of insecticide resistance in WA. These strategies include; identifying mites, rotating different chemical groups and reserving co-formulations or chemical mixtures only for situations where damaging levels of RLEM and other insect pests are present. For more IPM information see DPIRD’s Prevent redlegged earth mite resistance page and GRDC’s Resistance management strategy for the red legged earth mite in Australian grains and pastures fact sheet.
Article author: Cindy Webster (DPIRD Narrogin) and Dusty Severtson (DPIRD Northam).