Take-Home Results from Local Slug Research in the Northwest US

Literature Summaries and Citations

The information in the slug literature files offered below is compiled from peer-reviewed and local technical papers and reports, as summarized by our slug specialists. Please note that the literature reviewed (and not an exhaustive list) includes management practices, baits used, condition effects on slugs etc. These will be edited and more added to periodically, and as time permits. Only apply slug bait to crops currently listed on the pesticide label, and according to label directions. While the literature review currently primarily focuses on research done in the Pacific Northwest, worldwide literature will be included in the future.

  • Slug Literature Table that can be sorted by management practices, crop, subject area, etc. (xlsx)
  • References with Citation and Summary of Results (with PDF's attached for further reading)


Successes and Failures of Slug Control and Baiting

Draft 3-12-2016, A.J. Dreves
  • Choice of night for treating slugs was inadequate due to poor weather conditions (e.g.,  a freeze, heavy rain, too dry), hence bad weather reduces slug activity and feeding. Bait efficacy performs best on first day after application (60% control), then efficacy greatly declines.

  • Poor weather conditions arrived soon after bait treatment (24-48 hours after) which affected long-term treatment efficacy and control. Treatment applied, and soon thereafter heavy rains fell following bait application, which greatly reduced control efforts and slug feeding.

  • Excessive wind speed, extreme temperatures, lack of moisture, little condensation and low dewpoint affected slug activity, resulting in bait failure.

  • Insecticides applied for other pest organisms in field also affected natural enemies, such as ground and rove beetles that help control slugs.

  • Did not take into consideration the slug age or slug species in the field (egg, neonate, juvenile or adult stage) when choosing the treatment type at that time of year. Newly hatched neonates and young juveniles of D. reticulatum typically remain close to the ground/underground and feed on cotyledons or below-ground portions of plants. As juveniles mature they begin eating foliage. Neonates do not prefer baits. Neonates primarily eat algae, moss, fungus, and mold, but can eat vegetative plant parts. Liquid baits may be better suited for the very young slugs as they do not travel far as adult slugs.

  • By greatly disturbing the soil and its structure using tillage, can allow gray field slugs to feed undetected under soil clods, while destroying swelling seeds and very young seedlings prior to appreciable emergence. No other food is available but the crop.

  • Growers did not consider the high population of slugs remaining in previous crop before planting new crop. Consider treating harvested field if adequate number of slugs are present before planting a new crop. Have you personally determined a threshold level by experience?

  • Growers decided not to do a second application, when in fact monitoring revealed that slug populations increased after bait application, which possibly was due to new recruitment from hatching eggs, particularly in spring or change in weather; or slug populations went underground due to drying conditions, change from warm to cold, high wind levels, slow plant growth because of cold weather (fall), or low amount of dew at night or morning.  Slugs can go into aestivation and rest in cracks and burrows and later surprise you when favorable conditions return.

  • Numbers of slugs appear greater in establishing tall fescue when planted after red clover than in second-year stands.

  • Numbers of slugs appear greater in fall-seeded tall fescue after no-till annual ryegrass.

  • Numbers of slugs appear greater when no-till wheat planted into established fine fescue or when wheat harvested the previous summer.

  • Increased field residue, adequate drainage, lack of vegetation (allows greater freedom of slug movement), widespread organic manures, previous slug-susceptible cropping system increases slug prevalence and density.

  • Poisoned slugs from baits recovered when soil surface is close to saturation. The ability of slugs to rehydrate lost body fluids from poisoning by absorbing water through the ‘foot’ is possible.

  • Can’t expect control of populations, if slug density is too high. Get a handle on slugs early.

  • Growers did not start monitoring and treating for slugs early enough in fall, then conditions for treatment were unfavorable. It is important to get ahead of slug pressure, and monitor populations closely.

  • Immigration from adjacent landscape or weedy perimeter areas could add to slug pressure and affect success of bait.

  • Volunteer seedlings used to establish a new crop in the fall provide an early, abundant and excellent food source for slug populations. However, if these plants are removed with a herbicide to accommodate a direct seeded crop, all subsequent feeding activity may be shifted to the establishing plants that emerge in the row. The big questions is what practice is better? More research is needed here!

  • Management practices (such as susceptible previous cropping system, lack of burning, no tillage, installed tiling system, slugs carried into field by machinery, people or animals moving through the field; high insecticide use, reduced natural enemy presence) affect slug numbers.

  • Uneven distributions of slug populations in a field can affect field trial results.

  • Distribution of slugs/type of crop/cover crop/vegetation, adequate shelters for slugs, weed composition affect slug populations.

  • Soil type and pH play a role in slug population sizes.

  • Application of lime plays a role in reducing slugs.

  • Presence of predators and parasites of slugs help minimize populations.

  • Furrow not closed after seeding, can expose seed to slug entry and provide ideal habitat for a slug.