Looking at waxy bumps on a plant? We had this e-conversation with a gardener about his blue passion flower vine (Passiflora caerulea) but it would all apply to holly, euonymus, camellia, boxwood and lots of other plants this un-American pest can attach itself to.
J&S: Looks like one of the Ceroplastes species of scale. We'll call it barnacle wax scale (C.cirripediformis) although it could be a close cousin called Florida wax scale (C. floridensis, also called citrus wax scale). Differentiating between the two isn't critical right now since the immediate treatment is the same for both.
A scale afflicted plant shows the strain by paleness or losing leaves. Leaves or twigs may have spots or smears of sticky scale excrement called honeydew (at arrow, below) which then grows dark from sooty mold. Notice early and you'll see the scales as red crawlers or small white smears just beginning to get waxy. The scales you photo'd (thanks for the use of such clear photos) have been at work a while, sucking on the stems. They are adults with significant wax protection.
Armored scales such as wax scales begin life as mobile, unshielded crawlers but eventually settle down, attach themselves, lose their legs and (above, left) begin building a protective waxy coating.
Above, right: Once the scales are this old, pesticides may roll right off of them. At this point they are eating less than they were as crawlers, relative to their body mass so it's harder to deliver a lethal dose. They will produce eggs which remain under their armor . That double layer of protection -- "mom's" wax coat plus the egg case -- means the next time an insecticide can be reasonably effective is when the eggs open and the crawlers come out from under.
As with all insects, the older the critter the harder it is to kill. However, a direct dose of rubbing alcohol can work. Use a rag and alcohol or a cotton-tipped swab dipped in alcohol (as for mealybug, illustrated in What's Coming Up #77). You can even spray alcohol on the whole plant, but only if the plant's out of the bright light and you rinse it a few minutes afterward so it won't burn the foliage.
Follow up after a few days and then after another week or so, repeating the swab or spray where scales remain. Some always survive that were in tight crannies -- shielded by the plant -- or because they were not yet emerged from the sheltering egg.
J&S: Once it's cut to a couple of feet for winter, there's a lot less spraying and cleaning to do! Even during the growing season you could have pruned to remove the worst infested stems.
An option is to spray with a systemic insecticide. The plant absorbs that and then the insects ingest the poison as they chew or suck. Merit and Orthene are two examples, based on active ingredients imidacloprid and acephate, respectively.
Systemic insecticides are not very effective, however, on scales nearing maturity. Adults don't ingest enough to be killed but even if they do, eggs already in place under the dead scale's shell remain, protected.
J&S: Even so, follow up in late winter or early spring to derail a repeat performance.
The scales in this genus can host on a great many plant species and types, woody and herbaceous, tropical and temperate.** Young scales are not fixed like the waxy adults but can crawl off to live on adjacent plants including holly, Euonymus, Schefflera, Aglaonema, Hibiscus, citrus trees, Artemisia, banana, fig, English ivy, boxwood, apples, pears, cherries, peach, maples, magnolia and dozens more.
So be suspicious of any plant that was cozy with that infested passion vine. Discard those others, or cut them back and clean them well. Then watch carefully at the start of your next local scale season for sticky surfaces or pale leaves. Be ready to act earlier rather than later.
Essential follow-up: Same tale as for many other scales!
Indoors and in warm, no-freeze climates, be on guard for new wax scales in February. Watch for crawlers in mid- to late May in the garden (as far north as Ohio and New York where barnacle wax scale females survive winter outdoors and lay eggs in spring). In either case the date is variable depending on temperature. Watch for sticky honeydew or the tiny crawlers themselves. Use a soap spray, oil or other insecticide to kill these vulnerable young-uns. Over the next two to three weeks, repeat as appropriate to your tactic to kill later-emerging crawlers.
On a plant in a subtropical area or overwintered warm, wax scales can do this generational shift change more than once a year -- twice for barnacle wax scale, three times for Florida wax scale.
Passion flower (Passiflora incarnata) should be leafy all over (above, left, healthy and fruiting). The second vine (above, right) dropped leaves all during its scale infestation. Investigate when the leaf fall begins and you may fend off the trouble.