RLEM on the march

Author: Rebecca Barr | Date: 04 Jun 2015

Red-legged earthmites have been reported in SA and Victoria. 

PHOTO: Deanna Lush

Red-legged earthmites (RLEM) cause millions of dollars of damage to crops each year, and due to a cool start to the growing season causing the pests to hatch in April, now is the time for RLEM control.

SARDI entomology researcher Kym Perry says growers should not assume that preventative treatments applied at sowing will be an effective solution against pests.

“So far this season, there has been a number of reports from SA and Victoria, though the seasonal conditions aren’t particularly favourable to RLEM. With most growers generally applying seed treatments, especially to canola, there may be a tendency to be complacent,” he said.

“However, seed treatments aren’t always effective, so growers should really get out in the paddock and look for damage. Paddocks with a high level of risk should be the focus, and all canola paddocks should be inspected at least once if not more in the first month after seeding for pest damage.”

RLEM attacks most crops and feeds on all stages of plants, though is particularly damaging to seedlings in autumn. Early control of mites, before adults have time to lay eggs, is the most effective method, and reduces the chance of requiring a follow-up spray.

As with many pests in cropping systems, insecticide resistance is a real threat for RLEM. There are cases in Western Australia of RLEM populations with resistance to synthetic pyrethroids (SPs) including bifenthrin and alpha-cypermethrin as well as organophosphates (OPs).

“We are unfortunately in a situation where there are not a lot of insecticides available to us, which means growers always need to keep the risk of mites developing resistance front-of-mind. Almost 100 percent of the canola crops are being protected with the same seed treatment, which is unavoidable, but does increase the risk of resistance development,” Mr Perry said.

The GRDC provides the following tips for minimising the risk of resistance:

  • Spray only if necessary: It is best to only apply insecticides on paddocks that have a damaging number of pests.
  • Rotate chemical groups: Rotate between SPs and OPs between seasons and within seasons. When spraying for other pests, try not to use SPs consecutively.
  • Prevent hatchlings through early control in autumn, before adults can lay eggs.
  • Use insecticide seed treatments: Seed treatments allow lower quantities of insecticide than spraying.
  • Plan ahead: Controlling the crop and fenceline weeds can reduce the numbers for next season. Implementing a break crop with grazing can reduce numbers in problem paddocks.

More Information

Kym Perry, 08 8303 9370, kym.perry@sa.gov.au

Useful resources

GRDC Project Code GRS00154, CES00054, UM00049

Region South, North