Red Legged Earth Mite Resistance Here in the South West

Red Legged Earth Mites (RLEM) have long been a common pest in our legume and ryegrass pastures in the South West.

They are mostly a problem in autumn where high levels of mites in newly establishing seedlings can severely impact on growth and survival of the pasture. RLEM will hatch when conditions are favourable and live for about 8 weeks before laying eggs and dying. There are usually about 3 generations in a year. Spring will then see another heavy infestation before they lay a special diapause egg which can last through summer to hatch the following autumn.

Last year some resistance was found up around Capel to chemicals commonly used for RLEM control which mostly fall into two groups:

Synthetic Pyrethroides (SP) – eg Alpha Cypermethrin, Bifenthrin

Organophosphates (OP) – eg Omethoate, Dimethoate, Malathion and Chlorpyrifos

Due to this I undertook some RLEM resistance testing throughout the South West from Cowaramup down through to the Scott River.

The results of this testing conducted by the Department of Agriculture and Food showed that we have now got low levels of resistance throughout nearly all areas of the South West. 

Interestingly SP resistance is a genetic shift in the populations which is able to be passed down through generations of RLEM whereas OP resistance is a metabolic enzyme tolerance which is not yet thoroughly understood but seems to occur in single populations but not passed down.

How do we deal with this newfound resistance?

The most effective measure we need to take is to firstly spray only when you need to, then if spraying is required, rotate the chemical groups we are using for control to limit survival of resistant mites. Currently the resistance levels are occurring below the registered label rates so we need to ensure label rates are being delivered by making sure sprayers are calibrated and not spraying when the canopy is so thick that penetration won’t be delivering full dosage rates to the bottom of the sward. This may mean we need to temporarily move away from spring Timerite sprays and concentrate on the newly emerged hatchlings in early autumn once mites have been observed but pastures are less dense.

For more information feel free to contact me:

Brooke Anderson
AGRONOMY SOLUTIONS
brooke.inj@gmail.com
0427 997 869