Bayer CropScience - Pestspotter

Pest: Grey field slug

Identification
The grey field slug is a common and widespread pest which is instantly recognizable by farmers and advisers.

Symptoms
The classic symptoms of slug damage are seed hollowing and leaf shredding or complete leaf loss. Given suitable weather and soil conditions slugs can be devastating to establishing crops of cereals and many other crops. Slugs prefer heavier soils, and where the production of a fine, firm seed bed is not possible, the risk of slug attack is much increased. If crops can emerge quickly and grow away, they can escape the worst period of slug damage.

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 cause significant damage to all winter cereals especially if crops are late sown and emerge in cold wet conditions. Where pest pressure is severe whole crops can be lost. Cereals following slug favourable broad-leaved crops, such as oilseed rape, can be at greater risk.
Modern seed treatment insecticides, such as Deter, can help to protect cereals from seed hollowing caused by slugs, but these do not give any protection to the foliage above ground.

Threshold

FOR WINTER WHEAT
Monitoring recommendations
For further information on slug trapping and damage risk assessment please refer to HGCA Topic Sheets No.84 (winter wheat) and 85 (winter oilseed rape), available from the HGCA website [www.hgca.com].

To establish the need for pellet application on winter wheat 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.

A catch of 4 or more slugs per trap indicates a possible risk, where soil or weather conditions favour slug activity.