Get Pelletwise: Tough times ahead for arable producers if metaldehyde goes

Imagine a world without slug pellets. It’s not a happy prospect – but unless farming can reduce metaldehyde levels in water this autumn it is a very real one.

Water companies are unhappy that this popular slug killer is exceeding EU standards for pesticide residues in drinking water supplies. Unless levels fall, metaldehdye use could be severely restricted.

That might lead to more costly slug control, extra pressure on alternative treatments, the danger that they could also be restricted and, ultimately, the loss of all slug control options.

Impossible? Not if regulators have their way. “They want a sea change in the way slug pellets are used and they want it this autumn,” says Andrew Crossley, farm manager for the 2600ha Pemberton family operation near Cambridge and Peterborough.


“It’s not just about metaldehdye, it’s about the whole behaviour around the use of slug pellet products. If farmers fail to respond, their options for slug control could be severely hampered.”

He is well placed to comment, with oilseed rape taking a key place in the rotation at Trumpington Farm Company and Thorney Farms. As vice-chairman of the NFU eastern region combinable crops board he also has a good insight into pesticide politics.

Commercial agronomists agree. If metaldehdye users fail to improve application practices, a chain reaction of increasingly harmful restrictions could leave farmers with no worthwhile molluscicides, say David Wild, a Yorkshire-based Masstock agronomist, who is also responsible for environmental issues within the group, and Will Foss, a UAP agronomist based in East Anglia.

Levy-funded research endorses their comments. A major investigation into the likely impacts of possible pesticide restrictions highlights the dangers of losing metaldehyde.

If methiocarb use rises in response it could also start appearing in water, attracting new pressure. “This could potentially leave growers with no good molluscicides for the control of slugs,” the report states.

Based on work for HGCA and the Potato Council, which is in the late stages of completion, James Clarke of ADAS estimates that, if not controlled, the cost of slug damage to yield and quality in the UK is probably up to £200m in a bad year.

“Don’t imagine this is just about metaldehyde,” stresses Mr Crossley. “If farmers think they can carry on as normal and switch to alternative products they are wrong. The pressure will simply shift to those products, too. The industry needs to nail its behaviour with pellets now.”

Too few people are thinking of pellets as pesticides, he maintains. “Just because pellets don’t go through the sprayer it doesn’t mean they should be treated any differently.

“As an industry we need to get behaviour sorted out now, as we did with sprays through the Voluntary Initiative. Once it is in the mind that NSTS, NRoSO and CPMPs are a necessary part of farming, you’ve effectively brought farming up a level. We need to do the same with slug pellets.”

The Metaldehyde Stewardship Group’s code of good practice for the use of slug pellets might be enshrined in crop assurance schemes, he suggests. “We need joined-up thinking. As pellets are pesticides, why not link them into the VI and into crop assurance, so inspections focus on best practice for these products.

“Just because pellets are solid they shouldn’t be treated any differently to any other pesticides. You wouldn’t handle Avadex any differently to isoproturon, so why treat slug pellets any differently to cypermethrin?” he asks.

Recent farmer meetings have revealed just how unaware of the risk to pellets some farmers are, he notes. “Growers in Essex, with two wheats and an oilseed rape on heavy clay, were horrifed. ‘How can we grow rape without metaldehyde?’ they asked.”


Methiocarb is an alternative, he accepts, but comes at a significant price premium, has its own environmental issues and supply may not be able to meet demand from the outset, he notes.

He admits farmers find it hard to accept the EU’s arbitrary limits. “Yes, you would have to drink a vast amount of water to get anywhere near an intake that might have an effect on humans. But the limit is the limit and we have to live with it.”

He believes farming needs to stop thinking about acceptable residues and think in terms of avoiding all residues. “How good can we be, how low can we get the residues, that is how I think we need to be thinking so one product issue doesn’t just move on to another.”

Mr Wild echoes the points about switching to methiocarb. “It would potentially increase control costs, but that’s not the biggest worry. If metaldehyde goes the pressure will simply switch to methiocarb.” It is due for EU Annexe 1 review in 2017, but could succumb to environmental pressure sooner.

“Environmentally, it is not in the same league as metaldehyde. It is 10 times more toxic to soil insects and earthworms in terms of its LD50 value. It definitely kills earthworms; it’s a major reason why agronomists recommend it less these days – they want to do the right thing for the environment.”

Thiodicarb, another carbamate slug killer, has a similar environmental profile. So what about non-conventional options? “Caffeine kills slugs,” he accepts. “But it needs to be applied in 1000 litres/ha of water, which is not very practical. And while it is safe to mammals, it has very broad-spectrum activity, affecting many beneficial insects. Garlic kills adult slugs and eggs, too, but has not really been developed.”

His verdict? “If we lose the key slug control options arable cropping will look very bleak indeed on a lot of soils. Slugs can be a problem on chalky Wold soils; on heavier clay soils crops could be annihilated. You just wouldn’t be able to grow oilseed rape.”

Cereals and potatoes would suffer, too, as slug numbers escalated across the rotation. “I don’t think consumers would think much of potatoes riddled with slug holes.”


Improve the use of metaldehyde slug pellets now or risk a severely depleted armoury in future seasons, says Cambridgeshire farm manager Andrew Crossley

Fortunately, farmers are becoming more aware, he notes. “A lot of growers just didn’t realise such a small amount of product could cause a problem: One single pellet in 10,000 litres would push drinking water over the EU Drinking Water Directive limit.”

“Farmers are gearing up to act, particularly by ensuring that pellets are not directly spread into ditches and by taking care with washing-down procedures.” Getting messages to those who do not attend farmer meetings or read the farming media is one of the biggest challenges, he notes.

UAP’s Will Foss stresses the difficulties with cultural control. “Clearly, it is vital to try to place seed into fine firm seed-beds that restrict the movement of slugs and promote rapid even germination and establishment. But that’s often easier said than done, particularly for oilseed rape establishment.”

Non-inversion tillage and good subsequent consolidation can produce an extremely good seed-bed with minimal slug problems. “But in reality most autumns bring weather that results in less than perfect seed-beds. Whether its ploughed land ‘baking out’ resulting in cobbly seed-beds or wet conditions leading to rough unconsolidated min-till or seed direct-drilled into smeared slots.” Seed treatments based on clothianidin offer some early protection of cereal seed, but grain hollowing can still occur in high pressure situations and there is no protection of leaves.


Wise up on slug control

Catch up on all the key information and campaign news to keep metaldehyde at the forefront of the slug control armoury here

Alternatives to metaldehyde are limited. Ferric phosphate pellets have an extremely good environmental profile, but cost limits their use to high value vegetable crops and organic producers under derogation.

That leaves methiocarb, thiodicarb having been revoked for use in 2008. “It has label restrictions on use, including total dose and in cereals total number of applications, so limiting the loading of active ingredient on to a crop.” That makes careful and justified use of the methiocarb “ration” important to make best use of the permitted dose. “The same approach will be vital in 2009 to try to retain metaldehyde for future use,” he notes.

But methiocarb tends to be more expensive and has a poorer environmental profile. “It is one of the main reasons why growers and agronomists favour metaldehyde.

“One issue is the fate of methiocarb in relation to water, should its use become more widespread. It could become the next active ingredient targeted by water companies and regulators.”

For the future, some growers are looking to use precision farming technologies to adjust seed rates. By satellite mapping crop cover during the growing season, seed rates can be adjusted where there is a regular pattern of poor establishment.

If field walking confirms slug damage growers may be able to variably increase seed rate to help overcome poor establishment.

“There is significant pressure on farmers and agronomists to change the way they use metaldehyde slug pellets,” stresses Mr Foss. “Suitable methods need to be adopted immediately to have any positive impact.”

Label changes limiting the total amount of metaldehyde that can be applied to a crop, together with better pelleting practice, should help reduce levels in water. But a slightly different management approach may also be needed to ensure good crop establishment this autumn, he concludes.

Metaldehyde chain reaction

  • Greater reliance on remaining options
  • Possible product shortages
  • Big rise in cost of alternative pellets
  • New water and environmental issues
  • Pressure to restrict alternatives
  • No pellets for slug control
  • OSR impossible in some rotations
  • Up to £200m a year loss to arable profits

FW backs industry initiative

Farmers Weekly, Crops and FWi are supporting the “Get Pelletwise” initiative with a series of articles, academies, posters and forums over the coming months. In May our focus shifts to the impact restrictions could have. Find out more at and, where you’ll find all the key pelletwise information and articles.

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