I saw the other thread with the new additions having the aphids. So here's a couple of suggestions.
First of all, if you have an established garden or collection, regardless of whether Hen and Chicks, or other kinds of plant, you should
always isolate new plants from your garden or collection for a few weeks to make sure the plants are "clean". This is essential to maintaining a clean collection. In addition to isolation, a prophylactic treatment with an appropriate broad spectrum fungicide and broad spectrum .insecticide is additional insurance against many problems. Isolation is always appropriate, treatment is a judgment call.
Insects, such a mealy bugs and aphids: As a rule, these pests will come and go in their own patterns in your outside collections of semp's and jovi's. They will normally do little serious damage, but can harm the plants appearance at times. In most cases, you will have beneficial insects that will deal with the problem for you. If you have ever watched a lacewing or a lady bug chowing down on an aphid population, you'll know they are more efficient than are spraying (think hungry triffid on speed!
)
If you routinely or indiscriminately spray insecticides, then you kill the beneficial insect predators and indirectly promote the pests.
However, inside collections will likely need to be treated.
When choosing a treatment, you should first decide if there is a population of beneficial insect predators around. That will help you decide if you want to use something that will stay around for a while or do you want to use something that will solve the problem for a day or two (a pest population knockdown), then let the beneficial take over. For me here in western PA, that is primarily seasonally/weather dependent. Early spring or in the fall, there are few beneficials, so a longer term treatments are appropriate. During the summer, we have lots of beneficials, so if I must treat, I'll use something short term.
Short term, I like to use a pyrethrin based spray. These typically are mixed with an oil to kill insect eggs. These sprays work quickly and are short term. They are gentle on the plants but do not work over a long period of time.
Longer term provides protection against reinfection but requires some caution as some of the agents can do damage to some kinds of plants. Insecticidal soap is usually my first choice there, but has been known to damage some kinds of succulents. I have also used Sevin on sempervivum and jovibarba without problems. While I am not a fanatic about it, I try to take an organic approach in all of my gardening, so I avoid Sevin as a rule.
Systemic insecticides are also an option if you grow your plants in pots or limited areas. These are added to the soil and taken up by the plants so that the plant itself becomes toxic to the pests. I avoid these because I recycle my potting mixes and grow a lot of edibles in my garden.
I use alcohol against aphids and spider mites, which is moderately effective for the pests I have used it on. I cannot speak as to how effective it is against all of them. Alcohol is highly flammable and dangerous if sprayed. It is also a powerful solvent and can do some damage to some plants. I have never tried it on H&C's myself, but have used it on other things. I cannot advocate its use. However, spider mites are a tough problem and I reserve its use there. Alcohol does not stay around long, so its damage to plants is typically minimal if used sparingly.
I am an advocate of "layered" approaches when solving these kinds of problems. First, isolate. Second, alternate treatments with a pyrethrin and insecticidal soap on separate days is very effective. Third, a followup repeat treatment of pyrethrin and insecticidal soap will catch any lingering pests, done about a week later.
Don't worry too much, these are typically minor issues for outdoor sempervivum and jovibarba.
