By Russell T. Nagata By Russell T. Nagata ADVERTISING University of Hawaii at Manoa College of Tropical Agriculture and Human Resources Komohana Research and Extension Center, Hilo Shiny trails in the garden are warning signs that should be taken seriously
By Russell T. Nagata
University of Hawaii at Manoa College of Tropical Agriculture and Human Resources
Komohana Research and Extension Center, Hilo
Shiny trails in the garden are warning signs that should be taken seriously by all gardeners in Hawaii, especially if you plan to eat fruits or vegetables raw.
These are the dried out slime trails of the many slugs and snails that inhabit our gardens. While the slugs and snails appear to eat almost everything as they graze the garden buffet you carfully planted, they are not to be considered only a nuisance pest! The real danger is the microscopic round worms they harbored. The rat lung worm or nematode’s primary host is the rat, where it can survive and multiple. The worms are shed in rat feces, which the slugs and snails ingest and thereby acquire the rat lung parasite.
From slugs and snails, and possibly from their slime trail, the parasitic worms can be transferred to humans and cause eosinophylic meningitis, a debilitating disease that can cause suffering for years and can even be fatal. Although the rat lung worm cannot mature and multiply within humans and normally die with a year, if not fatal, the nerve damage it causes could last years after the parasite is dead.
In Hawaii about nine different species of slugs can be found in our gardens and over a dozen species of snails, both land and aquatic (fresh water), are found in the state.
All snails are not garden pests, so do not kill indiscriminately. Slugs and snails prefer moist environments that prevent desiccation, the main reason why they are more common on the windward side of the island. However, they are perfectly fine in dry environments if protected from drying out.
The African snail can seal itself in the shell and survive many months to years without free moisture, only to emerge in wetter conditions. Almost all slugs and snails are nocturnal, becoming active at night. Slugs and snails are all hermaphrodites in that they are both male and female, with each individual able to lay eggs and contribute sperm. They still need to find a mate to produce fertile eggs.
The most common slugs in Hawaiian gardens are the Cuban, or two-striped slug, semi-slug and the black slug. The semi-slug, a relatively new pest introduction to Hawaii from Southeast Asia, is spreading fast throughout the Big Island. The high rate of rat lung worm infection associated with these slugs and their presence near human food crops gives these slugs a high probability of infecting humans with the rat lung worm. As a precaution, wash all fruits and vegetable to be eaten raw very well and inspect for slime trails and very small individuals.
Control strategies for slugs and snail have bordered on the simplest methods to those that require a user’s manual.
One of the easiest methods is the use of slug baits, where you spread the bait around your garden according to label directions and the snails and slugs do the rest in finding the bait and indulging. Active ingredients vary, but the most common chemicals are metaldehyde or methiocarm (Mesurol) and iron phosphate. Caution must be used to protect children and animals from ingesting the bait, as some can be quite toxic.
Sanitation is a safe and cheap method of controlling slugs and snails, but may require more time to manage. By eliminating daytime hiding places, you discourage them to take up residence in your garden. On the other hand, you could provide hiding places such as rocks, boards, pots or cardboard around your garden under which they could hide. After a few days to a week or more, you can collect individuals using tongs or chopsticks for disposal. Many people have used beer in shallow pans set into the soil to attract slugs and snails. They are attracted to the yeasty smell and go to investigate, fall or crawl in and drown. Others have used yeast, water and sugar to attract slugs and snails as a cheaper bait than beer.
Several predatory snails have also been introduced to eat the large African snail, with the most common being the rosy predator snail. Get to know which are the good guys before you smash all of the snails in your yard, and if you have a good population of predators, don’t use poison bait. Other biological control methods include toads, which can eat many of the smaller snails and slugs, chickens, ducks and other birds. I prefer to manually collect them at night, drowning them in a container of soapy water and burying them the next morning. Slugs and snails will be out foraging a few hours after sunset and especially after an early evening rain.
Searching the Internet for slug and snail elimination solutions will result in many creative methods. Copper strips that you place around your raised planter beds or pots do work as a repellent. However, a determined individual will cross the barrier is it is dirty. Finally, one of the most creative, if not labor-intensive, is the building of a slug and snail electric fence using a 9-volt battery.
The labor comes in maintaining the two-wire fence at slug height without shorting the system out.
For more information on this and other gardening topics, please visit the CTAHR electronic publication website at http://www.ctahr.hawaii.edu/Site/Info.aspx or visit any of the local Cooperative Extension OVERSET FOLLOWS:Service offices around the island. I can be reached at russelln@hawaii.edu.
