Informative Slides on Slugs in the Pacific Northwest by Amy Dreves.

1. The often over-looked and unknown invertebrate
Amy J. Dreves
Phylum: Mollusca; Class: Gastropoda (Stomach-foot)
Oregon State Research and Extension I.P.M.
Entomologist/Malacologist
August 13, 2015 Soil Health & Slug Talk

2. 8-2015
Slugs are a serious issue
in PNW and Worldwide
Amy J. Dreves
ODA Plant Division
amber
brown
And snails are a problem also!

3. Correctly IDENTIFY who is doing
the crop damage

4. Low Tillage/High Residue
Lack of Burning
Bait Efficacy/ Poor Timing
Tiling/Drainage
Nightcrawler
presence stealing bait
Bad weather (eg., dryness, freezes)
Why such HIGH Populations
of Slugs in PNW?

5. foot
skirt
gonopore
or genital
opening
(under mantle;
eggs emerge)
radula
(mouth with
“teeth”)
upper
tentacle
(sight & smell)
lower
tentacle
(taste & touch)
pneumophore
(breathing pore)mantle
keel
(ridge)
pneumostome
(the mantle hides essentials; lung)
anus
(under
mantle)
buccal cavity
(slug mouth)
Slug Anatomy and
Identification
Eggs--------Neonates------Mating Adults

6. Slugs enjoy
cover crops
Crimson clover
Australian field peas
Buckwheat
Common vetch
Annual rye grass
Winter rye
Triticale
Cayeuse oats
Winter wheat
Sodbuster radish
AlleviatesoilcompactionSuppressweedsEnhanceseedbed
 Release Nitrogen
Buildorganicmatter
 Minimize erosion Reduce nitrate leaching  Reduce runoff
Gray field slug
Brown-banded Arion
European black/red slug
Large-spotted garden slug
Gray marsh slug
Greenhouse slug
SlugFamiliesthatfeedonagriculturalcrops::ArionidaeAgriolimacidae
Limacidae

7. Slugs also
enjoy grasses,
cereal grains,
& vegetables
Perennial Ryegrass
Annual Ryegrass
Tall Fescue
Fine Fescue
Orchardgrass
Bentgrass
Kentucky Bluegrass
1,500 grass seed farms in Oregon
 $50 million loss from slugs
 Avg. 30% loss/field

8. > 90% in PNW
Deroceras
reticulatum
Müller

9. Common Slug species in western Cascades
 Gray field slug (Deroceras reticulatum) & Marsh slug (Deroceras laeve)
– Most economically important slug pest
• European black/red slug (Arion ater)
• Dusky slug (Arion subfuscus or A. fuscus)
• Brown-banded Arion (Arion circumscriptus or A. fasciatus?)
• Black greenhouse slug (Milax gagates)
• Large spotted garden slug (Limax maximus)
1”
 variable in color, size, and shape; slime is white/sticky

10. Damage
• Scrape, shred, make ragged holes
• Kill apical meristem and destroy growing points
• Hollow out seeds
• Scar roots, tubers
• Create slime trails (the evidence!)

11. Slug Biology
• “Hermaphrodites” that cross-
fertilize (GFS) or self-fertilize
– they can give and receive sperm
and lay eggs
• Sexual maturity not until
several weeks-months from
hatching
– hatch as males; develop female
sex organs in a few weeks
• Life expectancy: 6 to 12 months
– sometimes 18 months to 2 years

12. • Eggs emerge from
“gonophore”
• Slug spend hours
depositing eggs (several hundred)
• Lay eggs in sheltered
cavities or under surface
mulch
• Clutches of eggs: 2 to > 40
• Clear to milky white eggs
– hatch in 2-4 weeks,
if laid in Sep/early Oct
– eggs may overwinter if
laid in late Oct/Nov
Egg-laying

13. SLUG Behavior
Alarm mode: contract to a smaller size, when disturbed
or when cold/dry conditions
Detect the presence of ground beetles by olfactory
cues: Become less active, produce excessive mucus, &
tail-wagging occurs
Neonates don’t move; eat differently than adults:
fungi- & algae-eaters
Weather can influence: Poison uptake and slug
recovery
Omnivores: feed on dead slugs, cat food, earthworms,
vegetation, sidewalks
Home-bodies: Travel only short distances per night,
unless unfavorable conditions
Aestivate: restrict their activity (months) when
conditions unfavorable
Nocturnal: night feeders
When irritated: Can thrive in moist
crevices, air gaps between clods of
soil, in vole holes, earthworm burrows
Travel per day:
A. lusitanicus = 9.8 ft (3 m)
A. hortenensis = 3 ft (1 m)
D. reticulatum = 9.8 ft (3 m), up to

14. 0
50
100
150
200
250
300
350
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
Rainfall(mm)
40.0
45.0
50.0
55.0
60.0
65.0
70.0
75.0
80.0
0–4inchesSoilTemperature(°F)
rainfall slugs soil T
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Onset of Fall
Mating and
Egg Laying
Onset of Late
Winter Mating
and Egg Laying
Egg Laying
ends-Juveniles
Present!
When are SLUGS active in mid-Willamette Valley?
Nightcrawler Activity Period
Agricultural
Research
Service 10yr data
W. Gavin et al.
Oregon
State
University
Slug Activity period stimulated
by Falling Temperatures and
Increased Moisture
Fall and Late Winter Egg Laying
Begin Hatching in Spring
SUMMER
Slugs Become Less
Active on Surface
as Soil Temperatures
Rise and Moisture Falls

15. Slugs move up as water table moves up
November 30
AverageWaterTableHt.
AverageWaterTableHt. December 30October 30
Agricultural
Research
Service 10yr data
W. Gavin et al.

16. Conditions slugs like…
• 100% humidity
• Negligible wind <5mph
• Cracks and crevices
• Surface debris
• Temp 40 - 70°F
• Light rain and fog
• Dark, shady, cloudy

17. Conditions slug dislike…
• Dry conditions
• Winds > 5 MPH
• Temp < 38°F, > 88°F
• Driving rain
• Sunlight

18. Minimum tillage favored Slugs!
Slug activity data based on four nights catch per month for the years 1992-2002, at sites in
Benton, Linn, and Marion counties ( Gavin, W.E., and J.J. Steiner, 1992-2002, unpublished data )
0
100
200
300
400
500
600
700
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
numberofslugs
minimal tillage no-tillage
**
**
**
**
**
** months with significant data
Oregon
State
University
no till
till
17 x more slugs in
no-till volunteer crop
than conventional plow.
(1996-1997 ARS trial)
1.5 x
Agricultural
Research
Service : 10yr data
W. Gavin et al.

19. Number of Egg Clutches
Average eggs per clutch 16.6 Average eggs per clutch 3.3
16
40
24
26
24
23
12
32
8 8
4
8
4
8
0 0
Residue positively affected Slugs!
Agricultural
Research
Service 10yr data
W. Gavin et al.

20. 0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
Evaluation Dates
MeanNo.ofSlugsperBlanket(12)
no sheep
sheep
Grazing sheep reduced Slugs by 44%
Oregon
State
University
Dreves et al.

21. 0
25
50
75
100
125
150
175
200
225
250
275
300
August September October November December January February March April May June July
No.ofSlugs
Tiled Field Un-Tiled Field
Better drained soils increased Slugs!
Tiles
No-
Tiles
( Gavin, W.E., and J.J. Steiner, unpublished, 2005, from: 1992-2002 Cropping System Database)
Agricultural
Research
Service

22. Delayed Emergence After Freezing Temperatures
30.0
35.0
40.0
45.0
50.0
days of month
2"soilT°F
0
1
2
3
4
5
6
7
8
9
10
slugspernight
soil T slugs
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 1
Feb Mar
Slug “Thaw”
Data based on ten freeze-thaw cycles over two year, 6 occasions. Freeze is interpreted as ground hard freeze at 2” depth.
Oregon
State
University
# slugs
temp
Freeze
4-5 day
activity delay
 Do not bait during Freeze Cycles, windy nights, and high
moisture conditions, cold temperatures
Delayed slug activity after a freeze-thaw cyclesoiltemperature(°F)
#ofSlugspernight
Agricultural
Research
Service : 2 yr data
W. Gavin et al.

23. Monitor for Slug Presence & Levels
• Slug ‘blankets’, plywood boards, white-rolled
roofing material or shingles (1 x 1 foot, white) or
secured black garden pots (relative sampling)
– Put shelter out afternoon/evening; check1-3d
after placement; count early morning hour
• Open bait stations
– clean area & bait
• Plant samples
(cold water extraction)
– (absolute sampling)
• Measure crop loss

24. Slug Blankets
18.75 x 18.75in
(LiphaTech®)
Cayenne
drench
Dreves
Open Bait Stations
Cold Extraction

25. Why monitor?
• Determine if slugs are present
– Increasing or Decreasing
• Estimate thresholds to decide if a treatment is
necessary…damage?
– Light = 0-2 slugs
– Medium = 3-5 slugs
– Heavy > 5 slugs
• Track development of slugs & stages over time
• Assess efficacy of treatments

26. We use the terms
“natural enemies,”
“beneficials,” and
“biocontrol agents”
synonymously to
refer to predators,
parasites and
diseases of pests
Cultural Practices
Biological Agents
Chemical Controls

27. • Manage field borders
– Decrease weedy and grassy borders or use as a ‘trap crop’
– Weedy species can be preferred, an alternative food source: plantain,
dandelion, shepherd’s purse and lamb’s quarter
– No-till fields can improve natural enemy populations
• Shallow plow and disking in spring (3 inches?)
– Crush and bury slugs, disrupt their pathways
– Row cleaners can move residue away from row
• Understand crop rotation cycles
– Choose appropriate crop rotation and cover crops: know the slug-
susceptible annual vs perennial crops that need attention
– Select crop varieties that are rated “excellent” for emergence and vigor
– Early or late planting to avoid when slugs are active, when juveniles feeding
– Foster early plant growth to “outrun” slug threat; get up quickly
Cultural Practices

28. A predatory nematode
(Phasmarhabditis hermaphrodita)
Fungal and bacterial
pathogens
Thrushes,
starlings, ducks,
and geese
Ground beetles
(Chlaenium tricolor, Pterostichus
melanarius Illiger, etc)
Encourage Biological
Agents
Sciomyzid
marsh Fly
(e.g., Sepedon spinipes
larvae)
• Scout for natural enemies
• Recognize them
• What can they do for you and
how do they affect slug
populations?

29. Malacophagous:
kills and feeds on
Mollusca, primarily
snails or slugs
Sciomyzid Marsh Fly
2014. Riverside, CA
Irma TANDINGAN DE LEY, Rory D.MCDONNELL,
Sandy LOPEZ , Timothy D. PAINE and Paul DE
LEY
2012-2013, Nurseries from the cooler part of
CA. D. reticulatum, D. laeve and L. valentiana
Phasmarhabditis hermaphrodita
(Nematoda: Rhabditidae)
Potential Biological Control Strategies
-with Bacterial associates
Nemaslug® (BASF Agricultural Specialties,
formerly by Becker Underwood,
Littlehampton, UK)
Sepedon spinipes larvae
Finds mucous trail

30. Chemical Control
(baits, pellets, liquids)
• Metaldehyde: contact/ingested; damages mucus cells
(e.g., liquid Slugfest, Durham, Deadline, Metarex)
• Iron Phosphate Granules: must ingest, seize feeding, 4-5d delay
before mortality (e.g., Sluggo, SlugKill); OMRI-approved?
• Iron Ferrous Chelate (FeEDTA; e.g., IronFist, Ferrox)
• Other: essential oils (e.g., clove, sesame, citronella, eugenol, pine
oil) as repellents,fumigant toxicity
• Methiocarb (e.g., Mesurol)
Band directly over/in a seeding row
Efficacy diminished over time & from weather
Choose the right night-60% mortality on day 1

31. Bait Rate? Timing
Durham 10
lbs/A
At planting or
close to crop
emergence
Sluggo 10-12
lbs/A
Summer or early
Fall (before rains)
* Dry soil
Slugfest 1.5
gal/A
Summer or early
Fall (before rains)
* Dry soil
Metarex 6-8
lbs/A
Late fall-early
winter; spring
* Wet soil
Deadline 10-12
lbs/A
Late fall-early
winter; spring
* Wet soil
Examples of
some baits
and
importance
of timing
*Attractant to slugs and a mammalian repellent (making them less risky to other animals

32. Weather affects
efficacy of baits
*persistence and
stability

33. Chemical Control Conclusions
• Multiple applications may be needed
• Maintain a 5-6 pellet per square foot density
• Success is variable: depending on season & weather (wind,
temperature, moisture), age of slug, species of slug, selection
of bait type, nightcrawler presence
Good Control:
– At DUSK
– SEPT & OCT (if temp. and field conditions conducive)
– MAR, APR, MAY (before too much egg-laying)
– Little to no wind (<5 mph)
– Temp. 15-19°C (>50 - 70°F), high humidity
– First night of baiting will be most effective
Poor Control:
– Late DEC thru mid-FEB; cold, too wet, little movement
– When slug pressure high and bordering vegetation around
field, then difficult for control

34. **Pick the “right” night for monitoring and for treating
**Avoid windy nights, high precipitation, cold temperatures
** Know where/when they are problematic
**Bait after a freeze & thaw cycle (3-4d after)
** Scout before damage occurs
*Don’t wait the following spring at seeding time to begin slug control
**Ideal to control as they surface in late Fall & emerge in spring

35. (Red Slug)
Institute a NW Mollusk PORTAL
slugportal.com initiated at Oregon State,
Crop and Soil Science Dept.
June 2016
• A blog exchange; Q/A * Outline factors that favor damage
• Survey slug species in varying crops * Slug biology, behavior, and life cycle
• Summarize literature * Grower stories: successes and failures
• Connect slug researchers * Report locations of mollusk problems
• List promising tactics
• Educate/Connect with the slug world
Reporting Tool
OSU Capstone
Project 44

36. Questions? Funding from:
College of
Agricultural
Science
NRCS, BCSWCD
Amy J. Dreves
Amy J. Dreves, Crop and Soil Science
Oregon State Research and Extension I.P.M.
Entomologist/Malacologist