Producer warning on slugs population explosion in South West
Slug populations are due to explode after the wet spring. Farmers and growers in the Westcountry are being advised to prepare for an increased slug threat later this summer after the wettest April on record created ideal conditions for slugs to reproduce.
According to David Glen, an independent slug specialist and former lead researcher with the Long Ashton Research Station, the current weather conditions are perfect for slugs.
"April to May is an important peak of the breeding cycle and with conditions as they are, slug activity will be very high – so populations are primed to increase significantly," he said.
Slugs represent a threat to all crops, but their potential to inflict economic damage is greatest in high-value crops such as field vegetables. The Horticultural Development Council estimates that slugs cost the sector £8 million a year in lost output. While in arable crops a single slug can kill up to 50 wheat seeds in the first week after drilling.
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The preference for winter-sown crops, the increased area of oilseed rape, and the trend towards lighter cultivation techniques have all helped to swell slug populations over the last 20 years.
Mr Glen warned growers not to be misled into thinking the dry conditions of the last three years would have reduced slug populations to safe levels.
He said: "Slugs are extremely resilient creatures, capable of surviving harsh environments before breeding rapidly when conditions suit. Growers should be assessing the level of slug activity in the run-up to harvest and in stubble after harvest to determine the size of the threat to next year's crop."
The threshold for wheat crops is four slugs per trap in stubble, but in stubble before oilseed rape, research has shown that just one slug per trap is enough to signal the need for action. Conventional practice has been to lay traps after cultivation, but before emergence of the next crop, though this can give a false impression of slug numbers, said Mr Glen. "Research has shown that disturbing the soil profile disrupts slug behaviour to the extent that indications might suggest a low population burden, when the opposite can be the reality."
Cultivation is an important part of slug control, though it will not remove the need for pellets in high-risk situations. "Those following a direct-drilling approach run a greater risk of sustaining slug damage," he added. "Cloddy seedbeds and wet weather around the time of drilling increase the damage risk whatever the method of cultivation, so be prepared to apply pellets at or around the time of drilling, ideally just after the crop has been rolled. The potential for damage is so great that waiting for activity to become visible means it is too late."
It was also important to use a high-quality pellet to get sufficient active ingredient into the slug for it to be fatal. Metaldehyde was the most cost-effective means of control available and capable of delivering exceptional levels of control when applied in suitable conditions.
Mr Glen stressed: "To be effective, slugs must ingest sufficient bait, otherwise they can recover. Some pellets, such as TDS from De Sangosse, contain an attractant and a feeding stimulant to ensure sufficient is ingested to cause paralysis.
"Slugs are free-roaming creatures capable of moving up to 20 feet a night, so it is important to achieve an even spread of pellets across the soil surface for adequate control."
Care should also be taken to avoid applying pellets to cloddy soil before heavy rain, as they will be washed down the soil profile and not found by the slugs.