PestFacts Issue 4, 2019

High Redlegged earth mite populations damaging crops

Unusually high densities of Redlegged earth mite (RLEM) (PDF 1.1 MB) have been reported across the lower Eyre Peninsula region, causing significant damage to canola, cereal and pulse crops and pastures.

We believe high RLEM pressure may reflect the concurrence of climatic conditions suitable for RLEM hatching (significant rainfall and on set of cool temperatures (range <16°C to <20.5°C) following a dry early autumn, leading to synchronous widespread RLEM hatching around early May.

Reports suggest seed treatment and some bare earth (PSPE) insecticide applications applied at sowing have resulted in inadequate control. This may be due to RLEM hatching later than the residual effect of PSPE insecticides (because seed treatments activity requires pest feeding, they cannot adequately protect seedlings against high population densities).

We recommend growers and agronomists in all regions monitor emerging crops closely for mite damage, particularly during the first three to five weeks post-emergence. Where insecticide treatment is warranted, select insecticides according to the GRDC RLEM Resistance Management strategy.

Notably, a property at Edililie applied a TimeRite® insecticide treatment to a single paddock last spring, and while all other paddocks have been heavily-affected by RLEM, this paddock did not require treatment. If considering Timerite® this spring, always only consider the current risk level (spring mite densities, and susceptibility of next year’s crop), not what occurred during the previous autumn. Note that Timerite® is only effective against RLEM, not other mite species.

Correct mite identification is crucial for effective control. Blue oat mite (BOM) (PDF 756.1 KB) has also been spotted in the same areas as RLEM, but one agronomist estimated 95% were RLEM and 5% BOM. Mixed mite populations occur commonly. BOM has a distinct orange-red patch on their backs that is easily visible under a hand lens, and typically feeds singularly or in small groups. RLEM typically form feeding aggregations of up to 30 individuals.

Bryobia mites (PDF 809.8 KB) have been reported in a cereal crop showing yellowing symptoms near Kimba. It was later confirmed that excessive herbicide residues, not mites, were responsible for damage.

If you are seeing earth mites of any kind, please let us know either through our Twitter @PestFactsSARDI, or to Rebecca Hamdorf (email: rebecca.hamdorf@sa.gov.au, phone: (08) 8429 0682) or Kym Perry (email: kym.perry@sa.gov.au, phone: (08) 8429 0738 mobile: 0421 788 357).

Sources of reports: Troy Maitland (EP Ag n Fert), Brad Foster (Bawdens Tumby Bay), George Pedler (George Pedler Ag), Nigel Myers (Landmark Cummins), Clint McEvoy (Landmark Streaky Bay).

Page Last Reviewed: 11 Jun 2019
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