The other day I noticed one of my favorite opuntias (Opuntia vul
However,



Back to the internets, where a search for (user whacks forehead with hand at this point) "cactus scale" points to this series of photos, confirming that cactus scale (the species Diaspis echinocacti, not the obvious, head-slap-inducing generic search term) is indeed the one infesting my plant and suggesting (but not clearly stating) those numerous smaller tubular shaped things among the larger round scales are another stage of development; immatures I suppose, but could also be the males although there seems to be an awful lot of them. So immatures is my guess.
What to do? Generally speaking, spraying contact pesticides on scale is not effective since their protective coverings shed water like a well-made roof and the chemical ends up killing the natural predators (lacewings and their larvae that generally keep the scale under control in my garden) which could bring the scale infestation under control. Systemic pesticides can work, but I recommend removal of the infestation before using any chemical control if possible. First, it feels so good to scrape off those little buggers. They can't move, so once they are detached from the plant they will die. By the way, a lot of the scale you see will already be dead anyway since they don't live forever but their little protective caps can remain attached to the plant for some time. Which brings me to the second reason to remove the existing scale from an infested plant: to monitor the ongoing or recurring infestation better. You can clearly see if there are new scale growing on the cleaned plant. If you decide to use pesticide, you will be able to judge it's efficacy by counting the numbers of scale before and after. These new scale will likely be coming from eggs left on the plant by the females you scraped off. Obviously, scraping off a scale infestation is only practical in the case of a small infestation. Larger problems can be cleaned off with blasts of water in certain cases.
So I decided to scrape off the cactus scale, and see if a reinfestation occurs before deciding to use a systemic insecticide on this plant. My tool of choice for this job is a cheap toothbrush (pick your favorite color), medium bristle with an angled handle that turns out to be especially good for getting into those hard-to-reach spots around the spines.
These last photos show the opuntia after the scale are removed; OK, I probably missed one or two of them but who's counting?
2 comments:
Interesting! I don't have an cacti, and I haven't seen any scale on my plants, which is nice. I also seem to have a lot of lacewings, so hopefully they'll do their job (and I am infested with asian lady beetles - maybe they eat scale along with aphids?).
Cool post.
Moe: UC IPM does list asian lady bird (Harmonia axyridis) as a predator of scale. Take care of them, and hopefully they'll take care of you and your plants.
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