Diagnosing slugs in crops

There are two slug species that are pests of broadacre crops the black keeled slug and the reticulated slug. Slugs are usually found on heavy soils and wet areas in the high rainfall area, slugs can especially be a problem in canola or pulse paddocks with high levels of stubble retention or rock piles, which provide protection over the summer.

Reticulated slug often light grey-fawn with dark markings; black-keeled slug usually black with a prominent ridge down the back.
Plants eaten to ground level or irregular patches or strips chewed from leaves

Suggested thresholds for control

  Oilseeds Cereals Pulses
Black keeled slug 1-2 per square metre (sq m) 1-2 per sq m 1 - 2 per sq m
Reticulated slug 1-2 per sq m 5 per sq m 1-2 per sq m

 

What to look for

    Plant

  • Plants eaten to ground level or irregular patches or strips chewed from leaves. Leaves can have a shredded appearance.
  • Poor canola or legume emergence from slugs feeding in furrows.

    Insect Adult

  • The reticulated slug is often light grey-fawn with mottled markings. The slug does not burrow into the ground, but survives summer under stubble, rocks.
  • The black-keeled slug is usually black with a prominent ridge down the back. It burrows to a depth of 20 centimetres (cm) or more.

What else could it be

Condition Similarities Differences
Diagnosing snails in crops Leave clear slime trails in the morning Presence of snails close to damaged plants
Diagnosing European earwig Similar damage European earwigs can be readily found hiding under rocks, organic matter in paddock

Where did it come from?

Wet conditions
Wet conditions
Contaminated stubble
Contaminated stubble
  • Pest slugs have become more of a problem since the introduction of no-till cropping and stubble retention.
  • Slugs are usually found on heavy soils and wet areas in the high rainfall area.
  • Slugs can especially be a problem in canola or pulse paddocks with high levels of stubble retention or rock piles, which provide protection over the summer.

Management strategies

Green bridge control
Green bridge control
Minimum tillage
Minimum tillage
important
  • Baits are more effective in controlling slugs and snails when there is no green material (i.e. weeds or emerging crops) to provide an alternative food source. Spread pellets when slugs are active after rain and to apply at recommended rates.
  • Baits alone may not provide sufficient control so it is necessary to carry out additional management practices.
  • Control of summer weeds ('green-bridge') results in fewer slugs being present in crops and also increases the effectiveness of baits by removing food competition.
  • Burning and tillage will reduce reticulated slugs but black keeled slugs are unaffected.

Economic and financial considerations

To assist in assessing the economic risk and financial costs associated with various treatment strategies go to MyEconomicTool

There may be other economic and financial implications that need to be considered when choosing a management option. These may include:

Pre-crop
  • Understand the risk of slugs being present and potential crop losses associated with slug feeding damage.
  • Assess the costs and benefits of taking preventative action such as removing a ‘green bridge’ or destroying stubble.
  • If seeding a cereal crop consider costs and benefits of increasing seeding rates.
In-crop
  • Compare the costs, benefits and risks of each management option against doing nothing.
  • Consider risk and associated costs or savings of no treatment or delaying treatment.
  • Ignore all previous treatment costs in assessing current management options.
  • Undertake a ‘what if’ scenario analysis to see what impact changing variables (e.g. grain price and seasonal conditions) have on the projected economic outcomes.
Post-crop
  • Consider using integrated pest management system – consider the costs and benefits of removal of stubble and green bridges, other pests and diseases and biological impacts.

View these economic considerations in more detail.

How can it be monitored?

  • Look for fresh trails of white and clear slime (mucus) in the morning.
  • Lay lines of slug pellets with a rabbit baiter. In infested areas, slugs are attracted to the freshly turned soil and pellets placed in the furrow. Very large numbers can be found dead or dying in the furrows or nearby.
  • Place wet carpet squares, hessian sacks or tiles on the soil surface with slug pellets under them. After a few days, dead slugs can be found under and around each square.

Where to go for expert help

Page last updated: Friday, 17 April 2015 - 11:19am