Wet Weather Increases Risk for Slug Damage

Moist conditions favour slug activity. Slug egg hatching should start shortly if it hasn't already. Juvenile slugs will be crawling around the damp soil looking for plants to feed on. Canola and soybean crops, especially those in no till fields with lots of residue on the surface are most at risk. Though corn is also a desired host, corn plants growing point is not exposed and therefore is not fed on so it can usually grow out of the injury, as long as slug populations are not extreme and the weather conditions do not continue to favour the slug to prolong the feeding period.

The juveniles can be the most damaging stage of this pest. Though planting as early as most did this year is usually a good strategy to avoid slugs before they hatch, this year has been warm and has also allowed the pest to develop earlier than usual too. If the rain finally ends and things dry up quickly we could avoid some injury. But if the cooler and wetter conditions continue, some injury may be unavoidable.

Slug can hollow out the seed causing poor germination and gaps in the stand. On larger plants, slugs feed on the leaves, leaving ragged holes causing a skeletonized appearance on leaves. Feeding damage can resemble that caused by hail and severe defoliation can result. If scouting during the day, you might see a silvery shine left on the soil or leaf surface as a result of their slime trails.

Slug control is difficult. The time that slugs are actually out on the foliage feeding is short and not all of the population is feeding on the same night, at the same time. Also, because they are not an insect, insecticide chemistries really don't work well on them. Anything else you may have heard of to spray slugs with is mainly doing one thing, acting as a dehydrator. That is, these "slug sprays" usually consist of some kind of salt base. Once they make contact with the slug, they dry the slug out just like salt dries out meat. However, for this to work, it must make actual contact with the slug. It isn't effective if it is sprayed on the foliage and not on the slug. The slug may crawl across the droplet and then soon after crawl across a droplet of dew washing the salt solution off.

There are always a few cases that I hear about where someone attempted to use a salt concoction to control the slugs found it to be successful. But for every 1 of these cases, there are at least another 3 or 4 that were unsuccessful.

The only true proven method of slug control is by cultural means. Tillage brings the slugs to the surface and exposes them to the sun and natural predators like ground beetles. It also reduces the crop debris habitat that the slugs hide in causing them to dry out and desiccate. At the very least, remove the crop residue on the soil surface, especially around the seedbed. Slug baits are available for field crop use, though the rates required at the prices they go for, make them uneconomical for most field crops.

Hopefully the sun will come out soon to dry things up and get the crop growing quickly so that this article can get filed away for use another year.

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