All About Slimy Slugs

June 2015

Erin Eagen Photo

Some parts of Southern Ontario have recently seen significant amounts of rainfall; leaving these areas with an increased risk of slug activity. Walking fields I have noticed more slim trails on the wet ground.  Here are some facts about slugs to help you identify a pest problem if it were to occur.

Susceptible Fields

  • No-till corn
  • Soybeans
  • Canola
  • Excessively high residue
  • Wheat with red clover underseeded
  • Newly seeded alfalfa
  • Fields following forage

Physical Characteristics and Appearance

  • Soft bodied
  • Legless
  • Grey in colour or mottled
  • Slimy covering, which prevents from drying out
  • Two tentacles on their head (likeness of a snail with no shell)
  • Average Length 1-3cm (up to 10cm)

There is one generation per year with two populations, thus one will mature in the spring and the other in the fall. Therefore there are two feeding periods with two different population timings. Slugs can survive over winter as eggs or their adult forms.

Optimal Habitat Conditions

  • Cool and wet periods
  • High humidity
  • Relatively cool temperatures
  • Debris (crop residue or manure) provides shelter from sun

When it comes to identifying slug damage many factors can contribute to a positive identification.

Possible Signs of Slug Damage

  • Above or below ground (dependent on moisture levels
  • Feed on germinating seed, seedlings, no preference on the plant parts
  • Generally lower parts of plants
  • Partly or thoroughly eating through leaves
  • Plant will appear ragged or skeletonized

Can resemble hail damage

slug 1slug 2

Scouting Tips

  • Active early morning or at night (nocturnal)
  • Look for gaps in your stand
  • Stripping of leaf tissue
  • Small holes chewed in leaves
  • Check under soil clumps and debris
  • Slimy silver colour trails

To attract slugs and confirm they are causing damage, you can create an artificial shelter (old shingles, would, moist cardboard) placed in the field. After a couple of days slugs will be living in the artificial environment.

There are a few methods which can help reduce the risk of having a slug outbreak.

Preventative Measures and Solutions

  • No action thresholds available
  • Planting into conditions that help crop grow quickly
  • Tillage to reduce crop cover
  • Expose slugs to dehydration and  various predators; birds and mammals
  • Presently no economically feasible chemical method for field crops

If you think you may have slug damage and would like more information and or confirmation contact a Veritas Agronomy team member.

You can find this information and more at: http://www.omafra.gov.on.ca/english/crops/pub811/13general.htm#figure13-1

http://extension.entm.purdue.edu/fieldcropsipm/insects/corn-slugs.php

http://ento.psu.edu/extension/factsheets/slugs-as-pests-of-field-crops