Extension Service Garden Hints

Less toxic iron phosphate slug bait proves effective

CORVALLIS - Over years of studying the effects of baits on slugs for the Oregon grass seed industry, Oregon State University entomologist Glenn Fisher is always learning more about battling slugs.

He and his colleagues have gleaned a lot of insight from years of work with slugs and slug bait in the field that might help home gardeners better cope with slug control.

After conducting trials with iron phosphate baits, Fisher and his colleagues have found that the less toxic iron phosphate containing slug baits are as effective as metaldehyde baits for controlling our common gray garden slug.

Only two chemicals are licensed and formulated into slug and snail baits for use on home gardens and on food and seed crops in the United States - metaldehyde and iron phosphate.

Iron phosphate slug and snail baits, originally used in Europe, have been registered in the United States since 1997. Products containing iron phosphate include: “Sluggo,” “Escar-Go!” and “Worry Free” slug and snail bait. These are sold as pelleted bait, typically applied to the ground around plants or crops. Iron phosphate baits have proven to be comparatively non-toxic around children and pets in comparison with those baits containing metaldehyde, according to the U.S. Environmental Protection Agency.

And Fisher’s research at OSU indicates that iron phosphate baits are as effective as metaldehyde baits for controlling our common gray garden slug.

Metaldehyde has been an active ingredient in slug and snail baits since the 1930s. Products containing varying concentrations of metaldehyde include: “Cory’s Slug and Snail Death,” “Deadline,” and “Slug-Tox.” These products are sold as granules, sprays, dusts, pelleted grain or bait and typically applied to the ground around plants or crops, to attract and kill slugs and snails.

Classified as a “slightly toxic compound,” metaldehyde “may be fatal to dogs or other pets if eaten.” The deaths of birds feeding in metaldehyde-treated areas have been reported in the scientific literature. These deaths were from the birds eating the slug bait, not dead slugs. The 4 percent pelleted metaldehyde bait, a concentration commonly sold to home gardeners is reported to be toxic to wildlife, according to the E.P.A.

Gardeners who are frustrated with battling slugs need to keep in mind that pest control using baits is very different from using an herbicide or insecticide.

“With baits, the slugs must actively encounter and ingest the bait for it to work,” said Fisher. “Since more than 90 percent of the slugs are underground at any one time, total eradication is impossible.

“Even when ‘good control’ is achieved, only about 60 percent of a given slug population is destroyed,” he said. “This usually suffices to protect the crop or garden, but often allows the population to recover over time.”

A crop or vegetable garden is at its greatest risk of slug damage when plants are young. It is best to bait at planting time or just before the seedlings sprout. If you wait until your vegetables or flowers get big, the slugs are less likely to come down off their plant food sources to consume bait.

“When plants are just about to germinate, your slug bait is the only food on the soil surface and they’ll be more likely to go for it,” said Fisher.

Cereal-based “mini-pellet” metaldehyde or iron phosphate baits such as “Sluggo” give the best performance record in western Oregon’s rainy weather.

The “tastier” the bait, the better the kill rate. In other words, cereal-based baits attract and kill more slugs than non-cereal-based baits, such as liquid slug baits.

Mature slugs are more easily killed with baits than young slugs.

Apply bait after rain showers, as slugs like to come out and feed then.

In addition to spring, fall is a good time to bait, because you can kill many of them before they lay eggs. But wait for the mornings to get damp, so the slugs will come out of their underground hiding places. Fisher recommends applying additional bait once more a little later in the fall to kill those little ones that just hatched.

Remove yard and garden debris, leaf litter and other excess vegetation, as these all prove to be refuges for slugs.

If you work the soil, it crushes slugs, buries them and disrupts their pathways.

Follow all label instructions and heed all label warnings. Don’t allow baits to contaminate the edible portions of plants.

By: Carol Savonen
Source: Glenn Fisher

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