Snails – control methods

April 2014. A problem with snails in Solomon Islands.

We have a snail problem and would be grateful to hear others’ experiences with the different types of metaldehyde formulations available. There are two formulations available to us:

• The common farinaceous bait which is a large granule spread evenly over the area to be protected, 50gm/m². The snail is supposed to be attracted to the bait and ingests a lethal dose of metaldehyde by eating the bait.
• A sand like formulation made up of tiny sand-like granules with the chemical on the surface. The tiny granules are spread evenly over the area to be protected (0.4-0.8 gm/m²) and the snail finds the granule by accident. The fact that the chemical is on the surface of the granule apparently makes it more available and it is claimed has an equivalent effect to a higher concentration of the chemical. This is a more expensive formulation but is it better than a true bait?

The moderator who sent the message asked to hear from members who have experience with these two formulations, in particular which is preferred and why.

There were several suggestions and comments:

1. Pellets coated in wax

A member said that in the CNMI they used a formulation that was lightly coated in wax and formed as a pellet so as to last longer in the field (perhaps #1 option). It worked very well and seemed to be more targeted to specific species and/or garden areas and away from non-target species including birds.

2. Cuba – Momordica

A member from Cuba mentioned that juice extracted from Momordica charantia is used to control Fossaria cubensis – a liver fluke in sheep.

3. Several types coompared

Wet pressed hard pasta type baits usually survive better in high rainfall areas such as the tropical Pacific islands. These are usually impregnated rather than coated with metaldahyde or carbamate pesticide (e.g, methiocarb). Some of these baits only require application rates of 3gm/m². There is a huge variation in use rate depending on the composition and formulation.

Pressed metaldahyde pollard or bran type baits will “blow up” as they absorb moisture and lose palatability and chemical content very rapidly; they are usually associated with home garden Do It Yourself products.

Coated chip slug control products are generally much less expensive, but are not as persistent as rain tends to wash the active ingredient off the chip.

Ferrous compounds e.g., ferrous chelates are not toxic to animals, but are not as effective in controlling slugs and snails. They are more repellent than they are toxic to snails.