Whenever we get a few days of rain during the summer, local snail and slug populations practically explode. The little nuisances show up on sidewalks, walls, windows, and worst of all for gardeners.. they eat hibiscus leaves and blooms! Snails & slugs are related species, and both thrive in high hot, humidity areas. Even without rain, automatic sprinkler systems can combine with warm weather to create ideal habitat for these critters.
They are not generally much of a problem in dry summer weather. But give the area a couple of weeks of soaking rain storms, or a little too much watering, and they will multiply like crazy. (Control measures effective for snails generally also work on slugs) They eat organic material, specifically: your plants. Ragged holes in leaves and blooms are signs of their dining habits.
Snails are hermaphroditic, which means that ALL snails can lay eggs. Many common garden species can lay an average of 80 eggs at a time, up to 6 times a year. Eggs are generally laid in small holes in soil or compost. The simplest snail-control method is to simply crush or pick up every snail that you can see. Gloves are a good idea, especially when picking up slimy slugs! Snails that have been picked up can be drowned in container of soapy water, or a solution of diluted household ammonia cleanser. There are a wide variety of snail & slug baits available, but is is important to carefully read the cautions on the labels.
Some chemicals are poisonous for household pets or children, and those compounds should only be used in controlled areas. Snail baits advertised as pet safe usually have iron phosphate as the active ingredient, and are generally safe to sprinkle around the yard and garden. (Sluggo is one brand available in local stores in the Houston area.) Baits are not particularly cheap, so wait for a few days when the rain lets up a bit, or that expensive bait may just be washed away. As with most pests, the best control programs combine several approaches. Snails need lots of moisture, so try to keep plant foliage as dry as possible, by using drip irrigation or buried soaker hose instead of sprinklers. (Water drops from sprinklers can also cause spots on delicate hibiscus blooms.)
Abrasive material such as pumice or diatomaceous earth, sprinkled around plants, will repel or kill snails that try to pass over it.
These materials generally soon degrade, or become ineffective when they are eventually covered with dust and dirt. Cedar mulch is said to be effective in repelling snails as well as a variety of insect pests. Copper flashing, foil, or screen can be used as a barrier. One theory is that the slime on a snail or slug’s foot may react with copper to create an electric current that repels or kills them. Copper sulphate solutions are sometimes used to
coat or paint tree trunks, forming a barrier that will last for months or years. A number of natural predators also eat the little pests, such as birds, snakes, turtles, and toads. Of course, some gardeners might find a yard full of toads and snakes to be minimal improvement over the original snail problem!
In some parts of the country, predator snails have been introduced to kill non-native “pest” snails, but this is done
under strict regulation and is not likely to be a practical solution for home gardeners. Traps can be another addition to the snail-fighting arsenal. One well-known type of snail trap is simply an open-top can or bowl of beer, set into the ground so the top is near level. Snails and slugs are attracted by the yeast smell, crawl in, and drown. Gross.. but somewhat effective in small areas. Sugar water can also be used, with about the same effect. Commercial traps using the same principle are sold in garden stores. An easier trap to maintain is just a board laid flat on the ground in a damp area. Put few pebbles or wood strips underneath to raise it about an inch. This creates a dark, moist area, and snails will congregate on the bottom of the board. Every day or two, lift the board and scrape off the snails to be crushed or drowned, as you prefer.
A combination of these methods should keep snails and slugs under control most of the time. If you can keep the initial population down, there will be fewer to participate in a population explosion during long rainy periods.