Growers need to prepare for high slug numbers this autumn after a mild winter together with a warm and wet spring breeding season has resulted in a large number of juvenile slugs being reported.
Independent slug expert David Glen says slug populations are being boosted by a big carryover of eggs from last autumn and also favourable breeding in April and May when individuals can lay up to 500 eggs each.
“Autumn-laid eggs will have easily been kept moist by the wet winter while the absence of any ground frosts means many will have remained viable coming into the spring,” he adds.
“Unless we experience a run of hot, dry weather it seems certain this autumn’s crops will be under pressure from the outset,” Dr Glen says.
Grey field slug
The slug species of greatest threat to combinable crops is the grey field slug (Deroceras reticulatum). It attacks all crops, is active at lower temperatures and is able to move across the ground faster than other species.
With populations active and visible, Dr Glen says growers should not apply slug pellets now, but be preparing to apply pellets up to a week before drilling in the autumn where populations breach thresholds.
“Any pellets applied before harvest are likely to have limited effect as populations will quickly rebound. Instead, growers should be planning to apply a wet-process pellet about a week before drilling begins, provided soil conditions are suitable for slug activity and the ground can be left undisturbed for three days after treatment,” he says.
Scotland’s Rural College pest management researcher Andy Evans says spring-sown cereals and oilseeds will largely be past the point of serious damage, but vegetable and potato crops, particularly those under plastic or receiving irrigation, are at risk.
His advice is to check field vegetable crops for early signs of slug damage and apply a quality wet-process metaldehyde-based pellet, such as TDS, if damage is seen.
“The important thing to remember about slug control in potatoes is that pellets need to be applied before the crop canopies meet across the rows so more pellets reach the surface where they can be located by the slugs,” Dr Evans says.