Prevent redlegged earth mite resistance
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Redlegged earth mite (RLEM) is a sap-sucking pest that attacks most crops and pastures as well as many common weeds and feeds on all stages of plants.
It is particularly damaging to seedlings during autumn and during years when the ‘break-of-season’ is late, or with late-sown crops and pastures as the mites are well established when seedlings emerge.
WA is the only state where it is confirmed that RLEM has developed resistance to synthetic pyrethroids (SPs - Group 3A), including bifenthrin and alpha-cypermethrin. Researchers say there are likely to be resistant populations spread right across the WA grainbelt and possibly into other areas of southern Australia.
RLEM often occur in situations with other mites, such as blue oat mites, bryobia mites and balaustium mites. It is important to correctly identify the pest present because these mite species respond differently to registered pesticides, and therefore insecticide products and rates need to be chosen accordingly. The wrong chemical treatment will cost money and only act to increase the selection pressure for further resistance development.
Growers who find redlegged earth mites (RLEM) that have survived insecticide treatments are urged to test for resistance and start planning spring control strategies.
The repeated cumulative exposure of RLEM to synthetic pyrethroids (SP) is the main factor behind the development of resistance. When a SP insecticide is used against pests such as weevils or aphids, RLEM also receive a dose of the chemical even if they are not the direct target.
University of Melbourne research indicates SP-resistant RLEM are up to 240,000 times more resistant to some SP insecticides than susceptible RLEM and this resistance is genetic – surviving through several generations.
On a positive note, tests have shown that WA’s SP-resistant RLEM populations do not have cross resistance to other insecticide groups, such as organophosphates (OPs – Group 1B), and can be controlled with these products.
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