The most troublesome invasive species in my backyard garden is the snail.
Yesterday morning, when I took out the buckets of shower-warning-up and vegetable-rinsing water to feed to my plants, I was horrified to find snails on my carrots, snails on my chard, snails on my potatoes, snails on my garlic, and especially snails on my tender pea plants.
The strawberries that were starting to get nice and red? Shot through with slugs (which are basically snails without the convenient handles).
On top of our wee little lime tree? Snails copulating.
This is not a situation conducive to effective gardening. Thus, the sprogs and I mounted an early (for a Saturday) morning raid on their dewy, shady stomping (sliding?) grounds.
Today's take: in excess of 500. (We lost count.)
Oh my. That's quite the snail infestation. Good luck with the eradication.
What kind of snails?
One advantage to domestic fowl, that. Pity about the zoning but it's hard to argue with the public health aspect.
Hereabouts it's caterpillars (too dry for snails) but the quail and mockingbirds (mostly; the grackles etc. do their parts too) do a pretty good job. Well, them and squash borers -- we're trying the shaving cream solution this year.
One trick that might work is the sticky-side-out duct tape. Caterpillars won't cross it, and that either keeps the little monsters on the ground where they're harmless or up in the foliage where they're bird food. Might work for snails too.
But, snails are so delicious.
Because you are vegitarian, escargot is not an option. So, as ethical persons, we presume you released the molluscs into a distant suitable habitat; garden of a PETA member perhaps. How will you deal with deer and bunnyrabs? Will you buy bloodmeal from the slaughterhouse to put out to deter them?
That's true that the morning after the dew... They eat everything ! All melons up to the leaves of grapevines. Especially need to weed around plants and to pick up up to the very small tiny snails. Good courage !
Ugh. My local snail population has exploded too. I hear that beer works...a little saucer for them to get drunk and drown in. I haven't yet tried it myself but I enjoy imagining all the tipsy birds staggering around after they've eaten their fill of inebriated mollusks. I am also trying to encourage frogs and lizards by providing some shelter and more moisture for them. I hear that they eat baby snails. Good luck to you.
Tip from a fanatical Northern California gardener: beer works, but what really does the trick is yeast. A bit of starch, some yeast, and water in a partially-buried dish come evening and you'll have died-happy snails and slugs by morning.
Also, drip watering vs. flood and getting rid of mulch around the bases of plants.
She confesses that her preferred solution was a French neighbor.
Some snails here, but mainly slugs. I'm going out tonight with a flashlight.
I had some more insect-y invasion, as well. I've been picking little winged black things, gnat sized, that have been sucking on my cherry tomato, and I've gotten rid of what I *think* are stink bug nymphs and an adult. (If they were assassin bugs, better I crush them then they bite me -- those things HURT.)
My lesson? I need to seriously work on attracting predators for my pests.
Cheap beer in saucers dug in so they are at ground level. Always surprising, but gratifying, to find two dozen bloated [marinated] snails in a 6" saucer.
Epsom salts sprinkled around the perimeter and again around the most vulnerable plants is said to be a stopgap measure. It is a fertilizer that soaks in after the rain so the effect of temporary but it might get you through a rough spot before other measures take effect.
People use these guys in citrus orchards down here. I hear garlic butter does wonders too but you probably have to cook them first.
I forgot all about fun with slugs and copper. You put a strip of copper at the line you don't want them to cross. If they cross it, it'll give them an electric shock. Ain't science grand?
I would try Clown Loaches. But of course, that would only work if the snails infiltrated your aquariums. Maybe if you made little reverse-SCUBAs for the loaches?
Besides copper tape (you can find it at the garden store), you can also try a layer of dry dichotomous earth around especially tender plants. It doesn't work well wet, so it has to stay dry, but it is too scratchy for them to do across. My experience is that handpicking works best, though!
You win. I've been gardening in San Mateo/Santa Clara counties since the late 60s, and while I've had snail infestations, never as bad as you report.
Laziest success: chickens in the garden.
2nd laziest success: paying small children 5 cents per mollusc.