Earth mites in autumn-sown crops and pasture

  • Red legged earth mites (RLEM) – all winter crops (see the insecticide resistance management strategy for RLEM)
  • Blue oat mites (BOM) – pastures, cereals, canola
  • Balaustium mites – canola, cereals, lupins
  • Bryobia mites – clover, canola, wheat, lupins
Objectives Pre-plant Seedling emergence – Vegetative – Flowering
Insects and damage

More information about earth mite identification and host preferences

Conduct risk assessment of each paddock based on;

  • mite history (from monitoring records in previous seasons),
  • fallow history/weediness,
  • timing of the break and
  • crop susceptibility to mite damage.

Good quality seed (especially canola) will ensure seedlings are vigorous and reduce period of susceptibility to earth mite damage.

Make decisions about the need for seed dressing, pre-plant or post-emergence insecticide treatment. Consider multi-pest risk and insecticide strategy that ensures rotation of insecticide groups to minimise the development of resistance in target and non-target species.

Weather conditions and time of day influence mite activity. Look for:

  • Byrobia mite in early autumn. BOM and RLEM occur in late autumn after cooler conditions have triggered hatching.
  • Earth mites usually feed on plants early or late in the day.
  • On clear, warm days, mites are active on the soil surface and at the base of plants. Bryobia mites prefer warmer conditions and may be found up on leaves.
  • In overcast weather mites are active throughout the day.

Damage:

  • Mottled and whitened cotyledons and leaves caused by the rasping and sucking of mites
  • Seedlings may wilt and die; others remain stunted and weak
  • Seedlings may be killed before they emerge
  • Damage more severe when seedling growth is slowed by cool, wet, or dry conditions

Mites can persist in a crop until November when they enter summer diapause. They do not cause crop loss in established crops.

Monitor and record Check paddock every 2-3 days for mites prior to sowing, at seedling stage and for at least first three weeks after crop emergence if mites are anticipated. Monitor longer if seedling growth is slow due to cool/wet conditions.

Inspect plants in 0.5 m of crop at 5-10 different sites. Ensure sampling covers field edges and areas of the crop at least 50 m from the edge

Record mite numbers and damage. Note: when disturbed mites drop to the ground to find shelter.

Natural enemies Shelterbelts and roadsides are a source of pests as well as natural enemies that may control mites in neighbouring fields.

Predatory mites, predatory beetles, spiders and ants will attack RLEM. Thrips and ladybirds attack BOM. A predatory mite, Anystis wallacei, was imported in 1965 for biological control. Where established it has caused significant mortality of RLEM. Its effectiveness is limited by its slow dispersal and inability to survive multiple cropping seasons.

 Cultural control
  • Grazing management of spring pastures to keep them short (<2 t/ha feed-on-offer), in the year prior to cropping can significantly reduce mite populations.
  • Control weeds well before seedlings emerge and/or apply appropriate miticide with herbicide when controlling weeds. Minimise weeds in fallows and around edges of paddocks.
  • Consider options for getting canola seedlings out of the ground as quickly as possible e.g. big seed, good soil-seed contact, planting as early as possible to avoid cold, wet conditions during emergence.
  • RLEM will survive on seedling chickpeas, lentils, and winter cereals but they do not reproduce on them. These crops, when grown prior to susceptible crops like canola, will reduce RLEM populations and consequently pest pressure on the canola. Manage broadleaf weeds in these non-host crops.
  • Planting field borders may be useful (e.g. wheat or oats may protect canola from RLEM movement from adjacent paddocks with high mite populations, or a border of lupins may act as a trap crop).
  • Check varietal susceptibility to earth mites under different situations.
  • Complex shelterbelts (made up of trees, shrubs and low-growing plants) provide habitat for a range of mite predators.
Thresholds Accurate economic thresholds are not available. Damage is a good guide for the need to control but pest numbers can give an estimate of damage potential. It is also important to be aware of RLEM hatching conditions (i.e. approx. 2 weeks with maximum weekly temperature below 21.5ºC).

Nominal thresholds:

  • Canola: 10 mites/100 cm2
  • Pulses: 50 mites/100 cm2
  • Wheat/barley: 50 mites/100 cm2
Pesticides Insecticide applications include:

  • seed treatments
  • pre-emergence bare earth
  • post emergence foliar – effective option where crop damage detected after emergence.

One well-timed spring spray in pasture destined for a susceptible crop (e.g. canola) in autumn can reduce carryover RLEM numbers. TimeRite® is an information package that provides farmers with optimum spray dates to control RLEM in spring. Use Timerite® to guide spray timing. Note: this timing is only appropriate for RLEM.

Levels of insecticide resistance in earth mites can vary between regions. Refer to the RLEM insecticide resistance management strategy for more information

Timing of control is critical to minimising crop damage.

  • Control the first generation of mites before adults lay eggs (within 3 weeks of mite appearance) This works well in years where there is a mass hatching in a single time interval.
  • If first treatment is delayed, a second spray may be required to control the second generation – especially in pastures.
  • Perimeter sprays around paddocks, to prevent movement of mites into fields from weedy fallows or weeds around paddocks, will also kill natural enemies.
  • Chemical sprays do not kill mite eggs, so apply sprays when most mites have emerged.
  • Consider the cumulative impact of pre-emergence, seed dressing, and post-emergence applications on beneficials. Refer to the impact of pesticides on beneficials table.

Pay close attention to individual pesticide labels as application rates vary with situations e.g. bare earth or post-crop/pasture emergence and with earth mite species.

Multi-pest considerations
  • Determine species composition before making spray decisions. RLEM, BOM, other mite species and lucerne flea can occur in mixed populations. The different species have different susceptibilities to insecticides.
  • Chemicals with specific activity against red legged earth mite (e.g. bifenthrin) can lead to a substantial increase in lucerne flea numbers through the removal of competition.
  • Lucerne fleas have a greater tolerance to pesticides than RLEM, so where both pests are present, control of RLEM is unlikely to control lucerne flea and could result in a secondary pest flare.
Communication Be alert to the likelihood of insecticide resistance in your region. Record control failures.

An Area Wide Management approach to the management of insecticide resistance in RLEM could be considered in regions with insecticide resistance.

Industry publications provide up to date regional information about pest activity in crops

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