Bayer CropScience - Pestspotter

Pest: Keeled slug

Identification
The keeled slug is a common and widespread pest which is recognizable by farmers and advisers. Keeled slugs, Arion spp and the grey field slug (Deroceras reticulatum) can all attack potatoes. Keeled slugs are less likely to be found above ground and are an important pest of tuber and root crops.

Symptoms
Slugs start to feed on tubers as they mature. They enter through small holes in the skin and hollow out feeding cavities in the tissue below. Damage is more prevalent on heavier soils in wet summers. Some potato varieties show partial resistance to slug damage, whilst others, such as Marfona and Maris Piper, are highly susceptible.

Life cycle
All slug pests are hermaphrodite and after mating lay eggs in batches of 10 - 50 in soil cavities and under stones or other debris. Up to 500 eggs may be laid in a season. After a few weeks, or longer in winter, the eggs hatch and grow steadily to maturity. It has been estimated that slugs can move at speeds of up to 0.007 mph !

Importance
Slugs can be an important pest of potatoes and growers are aware of the importance of minimising damage to tubers. The keeled slug, a primarily subterranean species, remains the most potent threat to the potato crop.

Threshold
To establish the need for pellet application, monitor for slug activity using baited traps. Where bait traps are used, use a foodstuff attractive to slugs e.g. chicken layer's mash which has proven to be particularly effective. DO NOT use slug pellets as bait in traps in these crops since they are a potential hazard to wildlife and pets.

Put slug traps out before cultivation, when the soil is visibly moist and the weather is mild (5-25°C). Traps consist of a cover about 25cm across, with a small heap (20 ml or 2 heaped teaspoonfuls) of chickens layer's mash (NOT slug pellets) beneath. In each field, nine traps (13 in fields larger than 20 ha) 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.