Inspect stubbles for slug pressure

With harvest underway across England growers are being urged to inspect stubbles for slugs ahead of what is expected to be a challenging time for autumn establishment.

“Our slug monitoring will begin in earnest once the oilseed rape harvest is fully underway, but initial inspections suggest slugs are present in potentially damaging numbers and there are also a lot of eggs resting in the soil profile just waiting for the right conditions to hatch,” says Scotland’s Rural College’s Dr Andy Evans.

His advice to growers is to follow established best practice guidelines and lay field traps once crops are cleared to determine the level of threat and the need for treatment. 

“The threshold level for slugs in wheat is four slugs per trap, but in oilseed rape research has shown that just one slug per trap is enough to signal the need for action. It is important to determine numbers in stubbles ahead of cultivations as doing so afterwards can give artificially low results,” he says.

Simon McMunn of pellet manufacturer De Sangosse says once threshold levels have been breached growers should consider applying slug pellets to stubbles or to cultivated ground ahead of drilling in a bid to gain the upper-hand.

“The reports we are receiving suggest slugs are highly active so if growers want to gain the upper-hand they should be prepared to treat early; ahead of drilling if needs be,” he says. 

“This has the added benefit of reducing the likelihood of diffuse losses as the ground is likely to be dryer,” he adds.

Although populations are at potentially damaging levels following the mild winter and favourable spring, Dr Evans suggests there is still time for Mother Nature to play a part in helping to curb numbers.

“If the summer continues and we have a run of dry weather lasting several weeks this will help to stem numbers by slowing breeding activity and drying out some of the eggs laying in the soil. But it is unlikely to remove the need for treatment in many areas of the country,” he says.

Once the decision has been made to commence with pellet applications he suggests growers use a quality wet-process pellet as a minimum standard to ensure good field persistence and efficacy rates.

“The wet-process pellets, such as TDS (metaldehyde), have been found to offer greater persistence and their quality flour ensures slugs don’t become bait shy as has been found to happen with some lesser quality alternatives.

“You really do get what you pay for with slug pellets. Mini pellets might be cheaper, but they don’t tend to last as long as wet-process where one application can be enough to see the crop past the critical stages,” says Dr Evans.

While pellets fulfil an important role in reducing slug pressure, Andy Evans is keen to point out that they do not excuse the need for good cultural control. Growers, he suggests, should seek to make life as difficult as possible for slugs by creating fine seedbeds that leave few places for slugs to rest up out of the summer sun and then roll them tight after drilling to make it difficult for slugs to pass through the soil profile.

“The value of a fine and well-firmed seedbed is often overlooked, but in high pressure years they can make a significant contribution to control efforts. In addition to promoting even establishment through good seed to soil contact, they reduce the hiding places slugs rely on during dry periods and leave them more exposed to predation by birds and other friendlies.”