FINDING a substance which first attracts a slug, and then encourages it not just to eat, but to eat enough to kill it, is no easy matter.
So its little wonder that, with the exception of the recent introduction of thiodicarb, two molluscicides – metaldehyde and methiocarb – have dominated the market.
Most manufacturers dont screen chemicals for molluscicide action, but test them only after they are proven in another, more lucrative sector of the pesticide market.
However, at the University of Wales in Cardiff, researchers have identified a number of additives, some derived from the beehive product propolis, which appear to improve the efficacy of methiocarb when included in the formulation.
For instance, 1% methiocarb with 1% additive killed more slugs and preserved more grain than 4% methiocarb on its own. The additives appear to be contact molluscicides in their own right, but may also act synergistically with methiocarb. Some of the compounds are also repellent to birds and so could add further value in terms of targeting.
Seed treatments may also reduce the impact on non-target organisms and provide a more convenient and cheaper method of control. On heavily infested, heavy clay soils in the Netherlands, seed treatments with metaldehyde and methiocarb consistently reduced slug damage in winter wheat and were at least as effective as conventional pellets.
Metaldehyde has been identified as a promising seed treatment. It is effective at 3.2g per kg of seed.