- Life of a Slug
- Research and Impact
- New Control Strategies
Slugs are mainly active above ground at night, whenever the relative humidity in their immediate environment is high, the optimum temperature ranges between 40 - 70°F, averaging 60°F, with moisture ample but not flooding, and the wind is negligible, less than 5 MPH. In seedling fields, slugs may feed in the furrow and destroy the growing point of the seedling plant.
Monitoring techniques for estimating relative slug activity as well as absolute slug density are described below to determine how many slugs are populating fields. Estimating crop damage in establishing and established grasses are discussed below. It is important to be able to distinguish the differences between damage caused by slugs and damage caused by other pests. There can be variability in slug numbers and crop damage in a field, so the more locations you monitor in a field, the more accurate determination of slug population numbers and damage level.
Examples of ‘slug shelters’ used to record relative slug activity, include: 18 x 18-inch slug mats/blankets, 12 x 12-inch ceramic tiles, white-rolled roofing material or shingles (12 x 12-inch), small flat plywood boards, bricks, 20 x 20-inch squares of hardboard covered with polystyrene, inverted black garden pots secured in ground, open or closed refuge stations with/without bait pellets in arena.
Commercial mats/blankets: Mats/blankets are composed of three layers with the top being metallic silver for maximum light reflection and the bottom consisting of black perforated plastic to absorb moisture. Between these layers is an insulating fabric enclosed to hold moisture within the mat. Mats are 18 x 18-inch (50 x 50 cm) and can be cut to smaller sizes. If conditions are dry, blankets should be soaked in a bucket of water then secured to ground surface. Blankets should be re-soaked at each visit, if dry.
Refuge traps (baited with slug pellets or unbaited with a cover over the top): Place a small wood board of any size on ground that has been cleared of vegetable. Mark with a flag to locate it. These traps should be examined the following morning (early) before traps are exposed to direct sun after placement. Bait (7-10 pellets) can be placed under a refuge trap (6 x 6-inch) or underneath mats/blankets, to poison the slugs and reduce the chances of slugs leaving the trap.
Standard uncolored Marley tiles (10.5 x 6 x ½ inch or 26.7 x 15.2 x 1.3cm): Tiles can be arranged on a 5 x 4 grid placed 34 yds apart (big study area) (South 1964).
Open bait stations (12 x 12-inch or any size)- Clear area from vegetation and add 3-6 bait pellets. A bait station consists of four pellets of either cereal bran-based bait with 2% metaldehyde plus 4% carbaryl or a standard metaldehyde. Keep the bait the same in the bait stations and always use the same amount of the bait in the bait stations (Fisher 2007).
Foam square pad-traps 25 x 25 cm (Hommay et al 2003): Pad traps are 13 mm thick made of polyvinyl chloride. Spread traps 3 m apart in a plot. Soil surface should be cleared of vegetation and watered over a 50cm square area. Counts can be made under pad and 12.5cm strip around traps to estimate activity on the ground surface.
Defined area traps (Glen et al. 2006), fenced beer traps and fenced slug mats: A plastic ring 25 cm high and 55 cm in diameter (0.25 m²) can be inserted 10 cm deep into the soil. The soil surface inside the ring contains 10 g slug pellets and the ring covered with black, light-impervious fabric.
One square meter areas: Set up monitoring areas in the right corner at the front of all test plots after sowing, and treat with 40 g Metarex. Check regularly 2x week), early morning or at night to see how much bait is still visible and record numbers of slugs present.
The Cold Water Extraction Process requires time (at least 5 days), labor, space and patience to count actual number of slugs in a soil-grass sample.
Pitfall traps can be used to assess the presence of ground beetles. Beetles with fall into the funnel attached to a jar below with alcohol.
A bottomless five-gallon bucket is driven into the soil with a mallet to a depth of 4 inches.
Prepare a dry mustard solution by adding 1 level Tablespoon of dried mustard to 1 gallon of water to create a mustard liquid solution. You can buy dry mustard powder in bulk. Prepare in advance.
Stir constantly with a spatula or whisk until solution is free from lumps.
Pour mustard solution into bottomless bucket over the soil at a depth of 1 inch.
A second dose of mustard solution might need to be added to bucket. Then cover tightly with a lid.
Total extraction time is approximately 30 minutes.
Replicate buckets by placing in several areas of the field.
Slugs, earthworms, and other invertebrates will leave the soil and can be counted on soil surface.
Pitfall traps can be constructed by digging a small pit that fits a small plastic margarine or yogurt container flush to the surface of the ground. Punch a small hole in bottom of cup for drainage, if rain gets in.
A funnel can be added that fits inside the container to reduce escapees. Large square hardware cloth can be added over cup to keep big animals out.
Place a roof, board or cover over the top of the container to provide darkness for the organisms captured and keep rain out.
Researchers studying earthworms have employed chemical expellants to drive worms to the ground surface for counting. It is rather quick.
Put out slug bait in late afternoon and return early the next morning to check for slugs or evidence of slime trails in a cleared vegetative area. Put several bait stations in the field. Scratch a small area (12 x 6 inches) of the soil surface (making it easier to see small slugs), and drop four to six pellets of bait on it.
You can cover the bait with a scrap of wood, a shingle, or a tile. This prevents other creatures from disturbing the bait, and the cover helps to keep slugs sickened by the bait from moving away.