Cacti and succulents are relatively pest-free plants, but, like any others, they occasionally fall prey to typical greenhouse pests like mealybug, scale, mites and white fly. Don't worry. Plants and pests go hand-in-hand. You'll constantly be bringing pests home with new plants and no matter what you do, you'll NEVER be completely free of them. The goal is control. Thankfully there are some simple, relatively toxin-free ways to help deal with the little nasties.
Probably the most common pest of cacti and succulents is the mealybug. There are several kinds of mealybug but the greenhouse, citrus, and occasionally long-tailed versions are the ones you'll encounter most often. They look like tiny, white sow-bugs and have the annoying habit of finding the most out-of-the-way spots on your plants. White, cottony masses are signs that they're reproducing…these are the "nests" that their little crawlers (nearly invisible) call home.
These buggers literally sap the strength of an infested plant and, with time and exploding numbers, can cause visible (though not usually fatal) decline.
Thankfully they are among the easiest of pests to control. Lug your plant to the nearest sink or hose and give the plant a good, strong shower. Mealys can be blasted off their hosts with a forceful stream of water. Another painless way to clean a plant up is with a cotton swab dipped in rubbing alcohol (isopropyl). Simply wipe off any that you see and then rinse the plant with clear water before returning to its spot. A couple of drops of dishwashing liquid to a quart of water is another weapon in the arsenal. The soap acts as a wetter, breaking down the waxy outer coating of many soft bodied insects, including mealybugs. Biological controls like predatory ladybugs and lacewings are also effective, but take some time to get their game on.
See signs of decline in your succulents for no apparent reason? Dump them out of their pots and check the roots. There is a mealy that makes its home underground and feeds on the roots of our plants. They are the worst as they are often not noticed until the plant has suffered. Off to the sink it went and got a thorough spraying until no insects or evidence of them was left.
I hate mites. First, you don't usually notice them until they've disfigured your plant. Second, they are attracted to….warmth and dry conditions–the same environment enjoyed by cacti and succulents. Third, they are tougher to control than some of the other pests. Plants that are otherwise stressed are particularly susceptible.
Mites are not really insects, but they are sucking monsters. On other plants it's common to find fine webbing…but not always on cacti and succulents. More commonly you'll notice brown, corky patches beginning to show up on formerly healthy plants.
Start your control by keeping a close eye on your plants. Scout for trouble. Keep them healthy and properly watered. Step two: bump your humidity up a bit and mist the plants once in a while (most will experience fog in their native haunts–it won't harm them). If you suspect an infestation of spider mites, use the "spray them off" technique discussed under mealybug.
It only seems fair that another of their ilk, a predatory mite, is one of the biological controls. It's a perverse little twist of Mother Nature's—and I like it!
After mealybug, scale is probably the most commonly encountered pest of cacti and succulents. These insects are like little armored tanks that clamp themselves to a leaf's surface and do their damage while hidden underneath a relatively impervious shell.
Not as easy to spray off, I usually use the rubbing-alcohol treatment to remove them by hand. A cotton swab or a small, stiff paintbrush will do the trick. They are very difficult to get a good handle on and it's always best to spot an infestation early. There are predator insects available but they are most effective if you can identify the species of scale that you're dealing with.
White fly round out the list of important pests to be on the guard against. They are, as their name implies, small white flies. While not common on most succulents, they seem to have a taste for Euphorbias, particularly the ones that have soft leaves. (I find this unusual since Euphorbias are characterized by their poisonous sap–the white flies don't seem to mind).
Parasitic wasps are the most enjoyable way to control these pests. This winter it took them only a few weeks to knock down a population of white fly that was threatening to get out of hand. Insecticidal soap sprays can be effective
People have been known to shake their plants and vacuum the insects out of the air. As a short term help to remove adults if may have some benefit, but I suspect that it does more for the psyche of the grower than it does for the plants!
Photo via missouribotanicalgarden.org
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