Spring control of redlegged earth mites
Spring has sprung. Growers and consultants are reminded to monitor for redlegged earth mites (RLEM) in pastures and to find out their specific Timerite® spring spray date, if spraying is necessary.
The timing of the sprays is based on a short window of the season when RLEM have stopped laying winter eggs (eggs that must hatch this season) and before female RLEM start producing diapause eggs (over-summering eggs able to survive until next autumn).
Controlling mites at this time means that the whole population can be reduced, leaving few mites to carry-over to the following autumn.
Growers who have not already obtained their spray date that is specific to their locality can do so (free of charge) from the Australian Wool Innovation (AWI) Limited website. It is here that growers may type the latitude and longitude of their property into the AWI TIMERITE® page to obtain their spray date and other useful information or contact AWI Helpline on 1800 070 099.
Studies by CSIRO have shown that spraying up to two weeks earlier or on the optimum spray date provides effective control of RLEM, however if spraying is delayed by two weeks after the optimum date the carry-over RLEM population into next autumn is much higher.
Farmers intending to spray paddocks should make the most of suitable weather conditions to go early or on time, rather than later than the predicted Timerite® date.
Growers are advised to spray only if they need to and rotate chemical groups to stop resistance developing in RLEM. Repeated use of synthetic pyrethroid insecticides or organophosphate insecticides such as omethoate and chlorpyrifos provides strong selection pressure for RLEM to develop resistance.
For more information on applying integrated pest management strategies when managing RLEM refer to GRDC’s Resistance management strategy for the redlegged earth mite in Australian grains and pastures fact sheet.
Growers who find RLEM that survive registered rates of insecticide treatments are encouraged to arrange for resistance testing to be conducted by contacting DPIRD entomologist Svetlana Micic, Albany on +61 (0)8 9892 8591 or 0427 772 051. The free-of-charge service, made possible with investment by the Grains Research and Development Corporation (GRDC), is led by The University of Melbourne, in collaboration with DPIRD, Cesar Australia and University of Melbourne.
Grazing reduces mite carryover in pastures
The level of grazing and quantity of pasture feed on offer (FOO) is directly related to the numbers of RLEM. Department grazing trials have shown intensive grazing in spring will suppress RLEM for the following season. However, it should only be used when the population of mites is above 5000 per square metre and FOO is more than 3t dry matter (DM) / ha. To reduce RLEM the pasture needs to be grazed to a FOO of 2t DM/ha or less for four weeks around the TIMERITE® period to achieve a significant reduction in mites the following season. For more information refer to DPIRD’s Controlling redlegged earth mites using intensive spring grazing.
Spraying of pastures in spring will have little or no benefit where pasture FOO levels are kept low, ie less than 2 t DM/ha, by grazing. Insecticides applied to control RLEM in spring pastures or legume break crops with FOO levels greater than 3t DM /ha will reduce their numbers and provide benefits by allowing increased spring growth and seed set and a much-reduced potential for RLEM carry-over into next autumn.
However, increased production benefits can largely be wasted unless the increased feed is utilised by strategic grazing management or fodder conservation. It is recommended that farmers should not spray all pasture paddocks but rather select paddocks for spring spraying based on FOO levels, future grazing feed management, level of required seed production and intended paddock use next autumn.
For more information on RLEM refer to the department’s Diagnosing redlegged earth mite page.
Article authors: Cindy Webster (DPIRD Narrogin), Dusty Severtson (DPIRD Northam) and Alan Lord (DPIRD South Perth).