Slug Biology and Ecology:Slug Biology and Ecology:A Key to FindingA Key to Finding

Effective Control OptionsEffective Control Options

Amber D. VallottonAmber D. VallottonVirginia Cooperative Extension-Rockingham CountyVirginia Cooperative Extension-Rockingham County

Crop and Soil Sciences Extension AgentCrop and Soil Sciences Extension Agentavallott@vt.edu avallott@vt.edu 540/ 564-3080 540/ 564-3080

“What exactly is it you dislikeabout slugs, Mr. Crabtree?”

……EVERYTHING!!EVERYTHING!!• Estimated that in years when favorable slug conditions

exist, stand loss can range from 50-90 %

Current Control OptionsCurrent Control OptionsMechanicalMechanical• TILLAGE

– To incorporate surface residue & weeds from previous planting, and any heavily applied manures to disrupt favorable habitat

• UNDER NO-TILL– Planting early to avoid peak time of slug activity– Use of row cleaners to remove residues from the furrow at

planting, strip tillage, and starter fertilizer

MolluscicidesMolluscicides• Slug Baits

– Metaldehyde Deadline M-Ps– Iron phosphate Sluggo

Control Options Control Options cont’dcont’d• Slug distribution often clustered vs. uniform, must scout for “hot

spots”

• Applied when slugs are at peak activity above soil surface good coverage is crucial!

• Slug may eat bait, but not get a toxic dose, so slug can recover

• Control only “buys time” allowing crop to outgrow feeding pressure

• Costs might be prohibitive for Deadline M-Ps ($15-20 /acre), but if pressure great enough alternative may be more costly

Pest Management OptionsPest Management Options• Any effective control strategy presupposes a Any effective control strategy presupposes a

thorough knowledge of the pestthorough knowledge of the pest– Biology

• Morphology• Life Cycle• Activity Levels in relation to the LC• Point where most vulnerable to control

– Ecological Relationships• Conditions favoring activity

– Feeding Behavior and Preferences in relation to crop and alternate hosts

Slug Biology/ Ecology 101: Slug Biology/ Ecology 101: OROR

A Brief Window into the World of A Brief Window into the World of the AMAZING Slugthe AMAZING Slug

Slug Anatomy: True or FalseSlug Anatomy: True or False

Does a slug have eyes?

Yes, simple eyes on Optic Tentacle

Does a slug have a tongue?

Yes, it is tooth covered, which is used like a rasp for grating food

Does a slug have feet?

Yes, it has a foot, which causes tell-tale “mucus trail”

Slug Life Cycle*Slug Life Cycle*

EGGS

JUVENILESJUVENILES

ADULTS

FEEDING JUVENILES

*One Cycle per year

Live ~12-15 months

FALL & WINTER

SUMMER

SPRING

Slug Life Cycle & ActivitySlug Life Cycle & Activity

April May June July Aug Sept Oct

ADULTS

EGGS EGGS

Corn Planting Soybean

Planting

SLUG JUVENILESADULTS

SOURCE: Ron Hammond, OSU, 2006

Feeding injury primarily in late-planted corn seeds, embryos, and seedlings (pre- and early-whorl stages)

If you can plant earlier, can avoid most damage since most juveniles have not yet hatched

CornCorn

Planted after juvenile slug hatch, so if slug pressure is high on early vegetative stages, there can be complete stand loss especially since growing point unprotected

SoybeansSoybeans

Conditions Favoring Slug ActivityConditions Favoring Slug Activity• Cool & Moist between 63-68 °F at 100% RH

• Tend to be nocturnal feeders, but during or right after rain are also active

• Dependent on available food sources, hunger, and distance from roost to food

Generalized Feeding BehaviorGeneralized Feeding Behavior• Movement by slugs is slow and costly because of the

loss of water as mucus trail

• Slug feeding strategy minimizes movement– Requires sampling behaviors & sophisticated learning

mechanisms– Used to assess a huge number of potential food items

• Smell crucial

• Food availability & accessibility also big factors

• Sequence of steps involved in feeding

Slug Feeding BehaviorSlug Feeding Behavior

LOCOMOTIONATTRACTIVE

SMELL ENCOUNTERED

MOVE TOWARDS

FOOD

FOOD TOUCHED W/ TENTACLE & LIP

IF ATTRACTED, SLUG FEEDS

REJECT B/C DETERRED Inhibition or

Food Texture Hard

FEED TILL FULL

DIGESTION

TOXIC?

AVERSION LEARNING

NUTRITIOUSPREFERENCE

LEARNING

Adapted from B. Speiser, “Food and Feeding Behaviour”, in The Biology of Terrestrial Molluscs (2001)

Slug Feeding PreferencesSlug Feeding Preferences• Slug diet varied plants, fungi, animals, and soil

particles

• Good evidence that slugs prefer specific types of plants

• Preferences– Learned behavior = test & either like or don’t like– Based partly on presence or absence of toxic plant

compounds (deterrent) Crops highly palatable & low SPC

– Softness or hardness of leaf surfaces

• Eat all plant parts at all stages of plant growth Fresh green, mature, dying, and decaying plant residues

Approaching Slug Management from Approaching Slug Management from a Biological/ Ecological Anglea Biological/ Ecological Angle

• In No-Till situations, do slugs prefer certain cover crops over others?

• If so, is slug activity higher in these cover crops and damage to subsequent crops greater?

• Other important questions about our cropping systems– Attractant vs deterrent to slugs?– Food composition Higher palatability or toxicity issues?– C:N in plant Greater satisfaction of nitrogen demand?– Provide more desirable habitat or shelter?– Offer more roosting sites?– Provide more protected egg-laying sites?

2008 Slug Research Plots2008 Slug Research Plots• Located in Mauzy• Two Main Rotations:

– Vetch-Corn (VC) and Rye-Soybean (RSB)

• For each rotation, three roll down dates for cover crop• Four replications within each rotation

• In each subplot, beer traps used as attractants

• Measured slug counts, slug length, and species

Roll-downPlanting Planting

April May June July Aug Sept Oct

ADULTS

EGGS EGGS

Corn Planting Soybean

Planting

SLUG JUVENILESADULTS

• As temperatures reached around 90°F, slug pop’s declined quickly in plots rolled down for several weeks (T1, T2), whereas # slugs in newly rolled plots (T3) remained more stable

• T3 cover provided more stable environment for slugs, whereas other plots had degraded

• T2 spike likely due to huge variability within T2 plots

Total number slugs trapped between May 28 and July 1 for each roll-down date.

• We see similar trends like in the RSB where slug populations declined quickly in plots rolled down for several weeks (T1, T2), whereas slugs in newly rolled plots (T3) remained more stable

• T2 more similar to T1 roll-down with only slight spike

Total number slugs trapped between May 28 and July 1 for each roll-down date.

• Overall, total number of slugs similar between the two crop rotations

• Variability between plot reps in each crop rotation accounted for differences

• This variability demonstrates that slug distribution may tend to be clustered and spotty in the field rather than uniformly distributed this has important implications for control application practices and the need to scout well before putting out bait

• Predominant type of slug was the gray garden slug (>97 %) with slight occurrences of the marsh and dusky slug

• Slugs consistently measured 1 to 3 cm in length, followed by slugs < 1 cm; very few were > 3 cm majority slugs trapped were juveniles

Future DirectionsFuture Directions• Lot of work needs to be done to understand slug

feeding preferences and its usefulness in developing control options

• Run second year experiment similar to last year– Sample slugs earlier to get better idea of early-season

pressure– See if any trends emerge when combining both year’s data

• Conduct another experiment– Plots comparing several different cover crop treatments– With/without N– Determine associated slug presence to better understand

feeding preferences

THANK YOU!THANK YOU!