Mark Your Calendar: the 74th Annual Oregon Orchid Show & Sale is April 22-23, 2017 in Portland, OR

Slugs & Snails

SlugEven those orchid growers that grow indoors on their windowsill can be afflicted with slugs or snails because once upon a time the orchids that they are growing were in a greenhouse exposed to more elements than what is found in your kitchen. Slugs and snails live in the medium and reproduce there, so they are not to be taken lightly. The very conditions that most orchids like are the same as what slugs and snails like: humid. You typically won’t see slugs or snails on your plants because they only come out at night, but you might see the damage that they cause with holes in the leaves. Some varieties of snail are very small, though, and the main damage they do is to the roots, so even if you don’t see leaf-damage, if you have an unhappy plant, it might be battling with snails.

The other difficulty is that the solution for slugs and snails that everyone is familiar with, salt, is quite damaging to orchids, so we need to resort to other solutions.

Bush snails (Zonitoides arboreus)pose a very big problem for orchid growers. They are very “invisible” other than their trails and the damage they leave behind. They are not attracted to snail and slug bait, but caffiene is a promising repellant and killer of the bush snail. Read a bit more here

Treatment Details Indoor?
Iron Phosphate Iron phosphate, the main ingredient in most “organic” slug treatments is safe to use around pets. The difficulty is that you don’t really want to put the iron phosphate in your orchid pot as it could affect the orchid’s well being (iron, as with most metals, has a negative impact on orchids) but there is nothing in the iron phosphate itself that will draw the slug or snail to it. Safe indoors, but not great for orchids.
Copper Tape Copper barriers are a popular technique for gardeners as slugs and snails won’t cross copper. This doesn’t do much good as the slugs probably live in the pot itself, among the roots of your orchid, so they don’t have to go very far to eat your plant. Safe indoors, but not very effective.
Diatomaceous Earth Diatomaceous earth can be hard to find and the orchid grower needs to be very careful in selecting the brand. Diatomaceoous earth is the skeletal remnants of microscopic diatoms left over from ancient, dried up lakes. These skeletons can be mixed in with your potting media or they can be the potting media altogether (this will work best in very humid, regularly watered, greenhouse environments – not so much so in the home). Because diatoms live in a variety of lake types, you need to be aware of where your diatomaceous earth came from. If it was from a salty lake you DO NOT want to use it with your orchids. Doing so could be very detrimental to your plants. Finding diatomaceous earth can be difficult in general. It is most commonly supplied in powder form, which won’t work for orchids as it would wash through the pot. Look for rocks of diatomaceous earth and try to find it from New Zealand or Australia as these typically come from freshwater lakes. If you’re unsure about the source, try it on one plant for a while (most orchids take a long time to show unhappiness). The way that diatomaceous earth works to kill slugs and snails is that it is very sharp and will cut them open as they crawl over it.WARNING! Breathing the dry dust of diatomaceous earth can be hazardous. Just as it slices up slugs, the fine dust can get in ones lungs and cause cuts – follow the directions for use on the package carefully! Safe indoors once dust has settled. Best to treat in a well ventilated area or outdoors if possible.
Beer! If you’re over 21, head down to your local grocery store and buy a can of cheap beer. This isn’t so that you can drink your snail woes away, but to bait and drown the pests in drink. This most organic approach to slug and snail control works for many people, though their orchid house can smell like a brewery. Don’t put the beer on the orchids or put the orchids in the beer. Instead, place small dishes (petri dishes would work well or shallow soy sauce dipping bowls) near the affected orchids. The smell should draw the pests out of their orchid pot homes and into the beer – where they will die. Safe indoors.
Metaldehyde Metaldehyde, as indicated above, is a very toxic substance that should be handled with extreme caution. Coupled with bait, it is very attractive to both pests (slugs and snails) and pets (cats and dogs). Simply reading the warnings on the package (which you should do!) will let you know just how toxic it is. It is not legal in all states, including California. Using baited metaldehyde in high humidity situations (such as a greenhouse) will result in molding of the product very quickly. This mold will invite fungus gnats and other critters that live off of mold. Also, after the product has been significantly wetted it can lose its effectiveness. Bush snails are not attracted to the baited metaldehyde products. Metaldehyde should not be used in or around the orchid pots and should not be administered to the orchid’s foliage. Many products with metaldehyde add carbaryl which is effective even when wet but is also highly toxic to people and animals. HIGHLY TOXIC! This is the most effective slug treatment but it is extremely poisonous for cats and dogs (and people) and the bait included in many metaldehyde products is attractive to these animals as well, so indoor use of baited metaldehyde should either be avoided or used with extreme caution.
Caffeine Promising research is showing that caffeine will KILL slugs AND bush snails. A mix suggested by First Rays for spraying your plants is 50/50 solution of strong coffee and water with a bit of rubbing alcohol to prevent molding (if you’re keeping the bottle for a while). Here’s a great research article on the use of caffeine on plants for slug prevention. Our testing has shown that about 800mg of caffeine in a gallon of water is effective in the treatment of slugs and bush snails. If you’re using caffeine pills to get this caffeine be sure to strain out the starch from the pills (using a coffee filter, for example) as the starch will stick to the leaves and damage the plant.  Safe indoors.