Recent wet weather has put emerging crops at greater risk of slug damage, growers are warned. But extra caution is needed if applying metaldehyde with the new limit on autumn applications.

Trapping and test-pelleting across the UK have revealed slugs are present in numbers that justify a treatment, advises independent consultant David Glen. “It’s been difficult to tell for the past three months because conditions have been so dry, so slugs have burrowed deeper into the soil. But they have now returned to the surface and are appearing in traps in stubbles. The field slug is laying eggs and will be making up for lost time.”

He recommends growers use traps – an upturned dish baited with chicken layer mash works best – to gauge populations as there will be some situations that will not justify a treatment. Just one slug found in oilseed rape warrants an application, while growers should apply pellets if four or more are found in stubbles preceding wheat crops. “Deep clay or silt loams in the north and west in particular are at risk,” advises Prof Glen.

East Anglian agronomist Colin Myram has seen plenty of damage in volunteer oilseed rape in Suffolk. He advises a pre-emergence application in rape crops will probably be justified. Test-baiting – apply a bout width of pellets across the middle of a field and inspect the next day for dead slugs – will reveal the risk in stubbles before wheat.

“But growers must adhere to new metaldehyde restrictions. The objective must be to apply as little as possible to stop it being washed through drains into water courses.”

Growers should restrict applications to 160g/ha between 1 August 1 and 31 December, with an absolute maximum of 210g/ha. “Applying 5kg/ha of a 1.5% quality pellet that’s small enough to give you plenty of baiting points allows leeway for a repeat application if necessary.”

Hampshire independent agronomist Tod Hunnisett has been surprised to see dead slugs in treated rape crops. “You assume the risk is lower, but they are resilient, and are coming back. The biggest risk for wheat is where it follows rape or beans. Here try to move the soil to upset populations and create a good seedbed, rather than treat prophylactically.”

In Goole, Yorkshire, grower and NFU combinable crops chairman Ian Backhouse has been cultivating more than normal and rolling twice to create conditions that will deter slugs. “The rape is through and looking good – we’re monitoring closely but haven’t had to treat yet. It’s imperative that every grower exercises extra caution when applying pellets this autumn and creates conditions that minimise reliance on chemical control of slugs.”

Stay within the limits

• Optimise cultural control – cultivate and roll to discourage slugs
• Trap or test-bait to gauge risk
• Keep pellets off headlands if possible
• Apply early, before it gets wet and drains begin to run
• Choose a low-dose product
• Aim for plenty of baiting points – 40/sq m is optimum

• There are three Farmers Weekly Academies with all the background and advice you need to help you steer crops clear of slug damage. BASIS and NRoSO CPD points are available if you complete the Test Your Knowledge section online at www.fwi.co.uk/academy.