Don't be sluggish about pre- seeding snail control

Picture of snails embedded in crop

Key points:

  • Cool moist autumn weather is ideal for baiting snails and reducing populations.
  • Baiting is economical if pre-seeding snail numbers are more than 40/m2 in paddocks to be sown to cereals and 20/m2 in paddocks to be sown to oilseeds.
  • Baiting before egg laying is critical, as it stops the snail’s lifecycle.

If snails are being easily spotted in paddocks, or were present in grain at harvest, now is the time to implement control tactics in the lead-up to seeding.

A recent snail distribution survey by the Department of Agriculture and Food WA (DAFWA) found widespread incidence of this pest across southern agricultural areas.

The survey was conducted as part of a national GRDC project - led by SARDI - to improve the management of snails and slugs, which are estimated to cost WA growers $3 million each year in control measures and lost crop production.

DAFWA researcher Svetlana Micic says killing summer weeds that provide food and a habitat for snails, burning or grazing stubbles and laying baits during early autumn can reduce on-farm snail numbers by as much as 95 per cent.

Snail hot spots

The 2013 DAFWA survey found the small conical (pointed) snail (Prietocella barbara) and the white Italian snail (Theba pisana) were the most common species in WA.

These were widespread in coastal areas, especially around Esperance, but were also found in significant numbers up to 200km inland.

The white Italian snail was only found on alkaline soils, whereas the small conical snail was found on all soil types.

Of the 178 sites surveyed in WA’s southern agricultural region, 33 per cent had snails considered to be at pest levels.

Sampling for snail numbers

Snails can be hard to see, especially the small conical snail, and it is good to check in stubble, around canola stalks, under rocks and around fence posts.

Paddocks that have received lime during summer and autumn should be inspected closely, as lime strengthens snail shells and increases survival rates.

A good way to find out how many snails are present is to use a 32cm by 32cm square quadrant and count all the live snails in it.

Multiplying the number of snails by 10 will give an estimate of snails per square metre.

Using multiple sampling points within paddocks will indicate the number of snails and where they are mostly found.

Critical control levels

The table below is a guide to economic thresholds for controlling snails in-crop:

Species


Crop

Oilseeds

Cereals

Pulses

Pastures

Small pointed snail

20/m2

40/m2

5/seedling

100/m2

White Italian snail

5/m2

 20/m2

5/m2

80/m2

Pre-seeding control options for snails and slugs

Weed control

  • Snail reproduction declines on bare ground.
  • Maintaining a weed-free zone about 2m either side of a fence line will help to remove potential breeding grounds.

Stubble management

  • Grazing will knock snails off stubble residue and stock may also trample them.
  • But grazing to control snails can be hit and miss and success depends on stock numbers and movement.
  • Grazing does reduce stubble ground cover and means less refuges for snails.
  • Burning stubble removes snail habitats and feed sources.

Baiting

  • Snails will only be controlled by baits if they are mobile and looking for food.
  • At a cost of between $15 and $85/ha, it is important that baiting programs are effective.
  • South Australian trials have shown that improving the calibration of fertiliser spreaders for bait application can spread bait more evenly and increase success rates of snail control.
  • Baiting is best done in early autumn when morning temperatures are low and dew forms.
  • Another good baiting window is after the first good germinating rains - when snails start emerging and seeking food.
  • First, check to see if snails are actively feeding on baits before spreading over big areas.
  • Killing mature snails before they lay eggs in autumn reduces the potential population build up for the season ahead.
  • Late bait applications are less effective, as the availability of more green material provides an alternative food source and juvenile snails (less than seven millimetres) are less likely to consume baits than adult snails.
  • It is important to bait along paddock borders, near fence posts and along fence lines and road side vegetation.
  • GRDC funded DAFWA trials to assess types of snail baits found those containing metaldehyde, methiocarb or Fe-EDTA were similarly effective.
  • But none of these baits killed 100 per cent of snails targeted.
  • There was no difference in efficacy between rain-fast and non-rain-fast metaldehyde baits.

The GRDC is continuing to fund a range of snail and slug behaviour and management research initiatives to improve integrated snail and slug control tactics and has a range of online resources available to growers (see useful resources section below).

ENDS

More information:

Contact:

Svetlana Micic, DAFWA Albany,
08 9892 8591,
Svetlana.micic@agric.wa.gov.au.

Useful resources:

GRDC GroundCover TV video featuring Svetlana Micic and Albany grower Scott Smith discussing snail management: http://youtu.be/HQVfn3bYLUE

GRDC Snail Management Fact Sheet: www.grdc.com.au/GRDC-FS-SnailManagement

GRDC Snail identification and Control: the Back Pocket Guide, Ground Cover Direct, free phone 1800 11 00 44 or: www.grdc.com.au/GRDC-BPG-Snail

February edition of Southern AgMemo in the ‘tools and services’ section of the DAFWA website www.agric.wa.gov.au.

GRDC Project Code DAS00127, DAS00134, YPA00002

Region West