You are here

Plant Health: weed, pest & disease management

Slugs

11 June 2018

View information sheet on Integrated Slug Control

Slug populations have increased in the past twenty years in part due to the increased area of Oilseed rape planted, rotations that include areas of non-cropped land and the ban on burning straw. It is estimated that slugs cost growers an estimated £8 million in damage, rejections and control per annum.

Risk Factors
Growers should always assess slug populations on land regularly used in crop rotations as well as rented land. Early assessment is critical to allow more time to incorporate effective control measures before a susceptible potato crop is established.Weed competition can also result in slow growth and prolonging the vulnerable period at establishment.

  1. Moisture and Temperature Slugs are dependent on moisture for activity, survival and reproduction. The optimum temperature of the field slug is 17oC but it will remain active even close to freezing.
  2. Soil Type –Heavy soils with high clay or silt content provide good habitats for slugs as the seedbeds on these soils tend to be open and cloddy allowing the slugs easy movement
  3. Previous Cropping –Slug damage is much greater after leafy crops such as oilseed rape than after crops such as potatoes.
  4. Crop Residues and other Organic Matter –Crop residues incorporated into soil or applications of manure especially in the autumn provide slugs with a food source and shelter.
  5. Cultivation and Seedbed Preparation –Non-inversion tillage increases the risk of damage by slugs. Ploughing is a good way of reducing slug populations.
  6. Other Agronomic conditions –Lack of nutrients, cloddy seedbeds, poor drainage

Integrated Approach to Control
For crops that are at risk of slug damage, the following measures should be taken:

Cultivations should be adopted to prepare fine, consolidated seed beds, which have three main benefits:

  • Reduction of slug numbers
  • Surviving slugs are unable to feed below ground on tubers because the seed bed restricts their movement
  • Tubers are in close contact with soil, sothey are able to take up moisture and nutrients rapidly, enabling them to grow quickly through the early vulnerable period.

The focus of applying pellets to potatoes often falls on in-crop applications but if there is an opportunity; cultivations in autumn (under suitable conditions) and pre-planting applications of pellets may help reduce slug numbers.

Historically the best time to treat a growing crop is between July and September when slugs are active. More recent studies reinforce the importance of these key timings.

Assessing slug risk
Put slug traps out before cultivation, when the soil surface is visibly moist and the weather mild (5-25°C).Traps consist of a cover about 25cm square, with a 20ml heap of chicken layers’ mash (NOT slug pellets) beneath.

In each field, nine traps (13 in fields larger than 20ha) should be set out in a ‘W’ pattern. Also concentrate on areas known to suffer damage. Leave traps overnight and examine early the following morning. A catch of 4 or more slugs/trap indicates a possible risk, where soil and weather conditions favour slug activity. If there are less than 4 slugs in the trap the risk of damage is reduced.

Summary of slug management options

  • Know what is coming - monitor slugs before planting
  • Think months in advance - consider pellets in the autumn
  • Choose cultivars less susceptible to slug damage if possible
  • Get at least one application of pellets on before crop canopy meets across the drills
  • Monitor slugs throughout the season if possible, although it is more difficult when the crop is at full canopy (mark where the trap is with a cane)
  • Avoid excess irrigation
  • Check for slug damage - lift early if possible

Metaldehyde Stewardship group www.getpelletwise.co.uk

For additional information from the AHDB Crop Divisions please see http://www.ahdb.org.uk/slugcontrol/

For results of trials on molluscicide efficacy see project 11120025