Issues with mollusks (slugs and snails) are common in the spring of cool, wet years and in reduced-tillage fields, particularly ones with cover crops. Slugs can pose much more of a threat to stands than snails. Many slug species feed on dead plant matter rather than on living plants and, therefore, do not feed on or damage row crops. Slugs will, however, feed on developing seedlings.
You can tell the difference between snails and slugs in several ways. First, snails have shells and slugs do not. Slugs hide under the soil surface or plant debris when the sun comes out, while snails stay on plants during the day. Slug feeding typically results in irregularly shaped holes on the edges of leaves, and slugs may cut plants in heavy infestations. Slug damage is often worse in situations where a furrow is not closed. This leads to “slug highways” on which slugs work their way down a furrow clipping several plants in a row. In some rare situations, a large number of snails on leaves can damage plants by weighing them down and bending them to the soil surface.
The question remains: what do we do about this? The answer, not much at this point. Snails and slugs are not insects, so insecticides do not affect them. Some baits containing metaldehyde or iron phosphate can be effective but are expensive and not always readily available. Baits can be broadcast at 10 to 40 pounds per acre but should be applied when no rain is forecast. If a replant is warranted, till the field to kill the slug population or you will be planting into the same situation.
The most effective management strategy for slugs is planning in advance. Scout at planting by pulling back plant debris to see if slugs are present. Slug issues tend to be worse in no-till fields and in fields following corn. Making row cleaners more aggressive at planting may help remove plant debris from the row, which may reduce injury on emerging plants. Ensuring that furrows are closed is important to avoid a slug highway and keep the slugs from clipping plants before they emerge. If possible, increase seeding rates by 5 percent to 10 percent to help reduce the impacts of lost stands. The best answer to this problem is hot, dry growing conditions that are conducive to seedling growth and bad for slugs.
In summary, slugs may cause damage; snails likely will not. Insecticides won’t help, so plan ahead with at-risk fields.