Fall Slug Control
By Mary Bardens; reprinted from the Tri-State Tribune, the newsletter of the Tri-State Hosta Society of NY, NJ, & CT
Did you know that fall is still egg-laying time for slugs? We tend to forget about them as the hosta leaves change color and head into dormancy. The slugs will be active until the soil temperatures reach freezing when they will go into hibernation until the spring thaw. So, until that happens, they will lay eggs. Mating will occur from August until mid-October with eggs laid about 30-40 days after that. Look for 1/8 to 1⁄4 inch sized gelatinous clusters of about 20- 30 spheres. Older slugs will lay larger quantities. The eggs may be hard to see as they can reflect their surroundings. When the eggs are near hatching, the spheres may become cloudy. Slugs love those piles of leaves, damp from heavy dews and fall rains.
Look for them under anything that will keep them cool and moist. Other favorite places will be flower pots, boards, cooled compost piles, at the edge of large rocks or under mulch. So the big question is what to do?
Eliminate their favorite spots: Clean up the old hosta leaves and other debris. Turn the compost pile to make it too hot to be attractive for them. Check under those flower pots before you store them.
Set a slug trap: They are attracted to any fermenting food: beer or a mixture of sugar, yeast and water. Sink a tuna can to 1” of ground level so they will crawl in and drown. If you put it flush to the ground you run the risk of drowning ground beetles which are a slug predator. Colorado State U. Entomology Professor Whitney determined that their favorite types of beer were Kingsbury Malt, Michelob and Budweiser. Check often to empty. Replace beer weekly. Commercial slug baiting stations are available. If you leave a flat board on the damp ground, you can scrape them off in the morning.
Go on a slug hunt: Late at night or very early morning, grab a flash light and bucket of soapy water to drop them into after hand picking. Slugs are nocturnal and love to hit the all night hosta diner. Watch for the little ones. Like teenagers, they are voracious eaters. You can even use a handheld vacuum to suck up the little pests, but you may want to warn the next person to use it.
Encourage a predator to hang out in your garden: Toads, turtles, owls, Mourning Doves, and Robins love slugs. And then there are some predators that we may not be too thrilled coming upon in the hosta bed that also feast on slugs: black ground beetles, opossums, shrews, wild turkeys, chipmunks, skunks, moles and Northern Ringneck snakes.
Iron Phosphate: Slug bait pellets made from this can stop slugs without poisoning birds, small pets, humans or
earthworms. Though they are not sure exactly why, iron phosphate inhibits the slugs from feeding. And, it is actually good for the soil. This is sold under the names of Sluggo, Es-car-go, and Safer?s Slug & Snail Bait.
Metaldehyde: This is a molluscide which means it is a poison that kills slugs and can be purchased in a form to spray on the hostas. It is very effective for killing slugs, but also earthworms and other things with which it comes in contact. Great care in handling, application and storage must be observed.
Ammonia Solution: A solution of household ammonia (1 part ammonia:5 parts water) in a spray bottle with the nozzle set on a direct stream and sprayed directly on the slug will kill it in a few seconds. This solution will not harm the plants.
Barriers: Copper tape placed around the hostas repels slugs because as they slime across it, it causes a toxic reaction like an electrical shock. But if they find a leaf lying over the barrier, they get in. A product called Slug de-Fence is composed of a low density polyethylene plastic and vacuum grade table salt. It repels the slugs unless they try to get over it, and then the salt gets them. Although, I?m imagining it may also look like you tried to wrap your plants with little trash bag fences.
Abrasive Materials: Eggshells, coffee grounds, sand, cedar shaving, hair or ash may be place around plants which scratches the slug?s bodies causing them to dehydrate. Diatomaceous earth can also be used, but it is a very fine powder and you must wear a mask to keep from inhaling it. But, these products must all be kept dry to work, so they must be reapplied after a rain.
Biologic Control: In Europe you may purchase the parasitic nematode Phasmarhabditis hermaphrodita which is naturally occurring in their soil. This is a microscopic worm that enters the slug?s body through natural openings and releases bacteria that multiplies and kills the slug in 4-16 days. It does not bother earthworms. It also has the ability to recycle and become part of the ecosystem in the absence of a host which would make it good for long term management. It is marketed under the name Nemaslug. But, don?t try to add it to your Thompson & Morgan order just yet, it?s still illegal here. Agricultural scientists from Ohio State and Purdue are doing parasitic nematode research to help protect crops in no- till fields which are most susceptible to slug damage. They are also evaluating the American parasitic nematode cousin, but so far, none is as effective at the European relative. They are compiling data showing the safety of importing nematode Phasmarhabditis hermaphrodita into our soil.
(From the Upstate New York Hosta Society Fall 2010 newsletter.)