15 September 2000

Stem the rising tide of slugs

Battling to keep crop pests

under control will be a key

activity this autumn. Over

the following pages we

provide some topical advice,

starting with slug slaying – a

vital activity after three

years of rising populations

and ideal breeding

conditions earlier this

season. Edward Long

provides some timely tips to

help you keep the slimy

pests at bay.

Edited by Charles Abel

IDEAL breeding conditions and plenty of summer moisture means that slugs pose a severe threat to arable crops this autumn.

Sharp rises in slug populations over the past three years add to the pressure, warns slug specialist David Glenn of IACR Long Ashton.

With no radically new control measures available farmers need to deploy every weapon they can against this notoriously difficult to control pest, he says.

"The cost of this cannot be accurately assessed but an average of £10m a year is spent on molluscicides with a similar amount paid in application costs.

"In a high risk autumn the overall cost is much higher. Yet despite the investment in chemical it remains the worst arable pest."

The pests prospects were boosted when set-aside was introduced and straw burning banned. Those measures improved soil organic matter levels, enhancing the pests ability to move around beneath the surface and survive the winter.

Slugs relish trashy, moist conditions. But even when soil dries out they wriggle down cracks and fissures in search of subterranean moisture. Even in a dry summer when they are usually lurking underground waiting for moisture before resurfacing to feed. Grave-diggers have found them 6ft down, in a drought year they could go even deeper, says Prof Glenn.

Wheat after oilseed rape is particularly vulnerable to attack, mainly because the pest finds rape seedlings appealing, so numbers are high after the oil crop is harvested. Trouble can also be severe after peas.

There are several slug species which affect arable crops, but the small grey field slug is the main culprit. Eggs are normally laid in spring and autumn, but in wet seasons it can continue through the summer.

"Damage to wheat can be severe but early attacks can completely wipe out oilseed rape crops," Prof Glenn says.

"Slugs develop a taste for tiny seedlings which they regard as a delicacy. They can be nipped off at ground level as they emerge, usually the first indication that something is wrong is when there is no sign of the crop."

Potatoes high risk

Potatoes are a high risk crop. A prompt harvest reduces the window of opportunity for slug attack, reducing the chance for the pest to invade tubers. In areas or soils where the pest is a constant threat growers should try to avoid planting susceptible varieties such as Estima, Marfona and Maris Piper, Prof Glenn advises.

Dont let slugs eat into your profits this autumn. Although there are no new weapons to delpoy, a closer focus on control should improve crop protection, say experts.