Hi. I have an indoor schefflera plant which is about 12' high, with a recurrent infestation. I first contacted you about the same problem about 5 years ago--I'm trying to see the history but many of the earlier communications are no longer viewable. The critters are what you originally surmised were soft brown scale. You commented that a characteristic of these were yellowing, die-back, honeydew and black sooty mold; I see all of those things (a LOT of honeydew) except for the mold. My understanding was that you recommended removing them with an insect soap. I have done that many times over these years; it helps for a period of time--at one time for maybe a year or so--but then they're back. A month or 2 ago I very thoroughly did the entire tree, which was badly infested; then every couple of weeks a few are back and I have to do them again. So. I am using Safer Brand Insect Killing Soap, spraying the surface (most bugs are on the tops of the leaves, some on bottoms; a few on stems) and wiping off with paper towels. Is there a different product I should be using? Which might leave a residue to prevent their return? Or which would actually KILL them, rather than just remove them? As it is a houseplant and I have cats, I don't want to use anything too toxic. You had also recommended getting the tree into more light--I have enormous windows, but it likely doesn't get enough light. Does this make it more susceptible, or is that just a separate issue? I am attaching a photo which shows a few of the bugs. Thank you!!
Fortunately, we can see the prior questions you have submitted over the years regarding your scale issue on the Schefflera. Sooty mold may not be as common indoors as it is outdoors on honeydew, probably because fewer spores circulate indoors without getting filtered-out by central air vent filters and less exposure to outdoor air in general. Honeydew will be present regardless, and is your prime indicator of an active scale infestation (as opposed to dead scale still stuck on the plant). Given how long you have battled this problem and the lack of success in using insecticidal soap or horticultural oil, we recommend trying one or two different approaches.
If possible, put the plant outside for the summer. (Given its height it would need to be gently tied to something to keep from falling.) This will allow it to bask in the high humidity and brighter light to improve the plant's health. Do not situate it in direct sunlight; rather, total shade that still has decent ambient light would be ideal. Bear in mind that the warmer temperatures will likely cause the potting soil to dry out faster than it does inside, so monitor it for watering needs. Outdoor living will also allow natural scale predators to discover and control the scale population. It is not uncommon for pest outbreaks to be completely controlled in this way by the time plants come back inside for the winter in October.
The other option is to switch to using a systemic insecticide. One candidate ingredient, acephate, would require spraying, so the plant should be sprayed outdoors and kept outdoors for at least a few days while the spray dries. The other candidate ingredient, imidacloprid, is granular and can be applied indoors or out. (The product will be labeled for use indoors, unlike other systemics for use outdoors.) It is mixed into the soil surface and watered in to start dissolving and releasing the ingredients. (The granules will not disappear entirely.) For either treatment, you can can opt to keep the plant outdoors the entire summer while the pesticide goes to work.
The scale are likely returning because, despite your best efforts, there are some that are escaping detection. This is normal; many houseplant pests are very good at hiding in plant crevices where they are not reached by sprays or alcohol swabbing. If there is no great sentimental attachment to a heavily infested plant, it's usually much simpler to discard it and start with a fresh one.
We understand that you want to limit harmful chemical exposures to your household. However, Schefflera itself is not safe for cat chewing or ingestion, so any nibbling could result in harm regardless of insecticide treatments used.
Houseplants receiving too little light is another common issue among many indoor plant growers. Human eyes are so good at adjusting to varying light levels that it is difficult for us to judge what light levels are truly dim or adequate because of this. Light intensity falls off dramatically with relatively small distances from the light source (in this case, a window), so even a couple feet closer to a window can make a significant difference in the light a plant can make use of. Ideally, this plant should be directly in front of a north or east-facing window, or fairly close to a south or west-facing window. Spots immediately next to a bright window, on the side out of the direct path of light (since light travels in a straight line), are much dimmer than we think they are. Lack of sufficient light - which is essentially plant "food" - is one main reason some indoor plants fail to thrive. Tolerance to lower light levels can be excellent for some plants, which is why they can survive for long periods on too little light, but eventually it can take a toll on their resiliency and health. Pests can take advantage of ailing plants as they are easier to overwhelm.
If you wish to keep this plant, the more effective action for now would be to find a location to grow it outdoors for the summer. Pesticide or not, this should both help the plant recuperate and reduce the scale population. Come late summer, you can consider a preventative insecticide treatment prior to bringing it indoors to clear off any straggler scale insects.
Thank you for such a thorough response, Miri! It would be extremely difficult to get it outside; it has 3 or 4 main shoots, two of them 10' - 12' high, and the spread of leaves is probably 8'. I could bundle them together some, but it's still a big guy. Once outside, I'm not quite sure where to put it; we live in an old factory building near Penn Station, with no yard or anything. On one side of our building we have a steel column I could tie it to, but it would be exposed to direct sunlight from early morning until probably 2:00 or so, and you say that would not be good. So maybe I'll first try the imidacloprid, and continue to clean it off every couple of weeks.
You said that outside it shouldn't be in direct sun, but (I believe) you are encouraging MORE direct sun if INSIDE. Is that correct? Right now it is in a southwest corner. There is a big window in each wall, 3' from the corner. The center of the pot is out about 2' from each wall. So parts of it get direct sunlight for much of the day, and a lot of it gets some amount of direct sunlight; parts of it never get direct sunlight. I could move it so it is smack in front of the west window; would that be beneficial?
I water it when the topsoil feels dry, which is only about every 2 weeks. It's in a 22' pot, and takes 2 gallons or a little more. Should I be watering it more?
We understand; lack of outdoor growing space can be frustrating. In that case, you could consider using an indoor plant grow light suspended above it to provide supplemental light, though this could certainly be equally challenging given its height. Yes, brighter light inside may help, though from your description it sounds as if it is receiving more light there than it appeared in the photo of it in the corner. You could experiment with moving it a bit closer to the window, if there's room.
It's best to gauge the soil moisture further down than just the surface, as this will always be the first to dry while deeper roots remain damp. About a finger's depth is better, especially given the size of this pot. Much smaller pots (say, 3" or so) can be often be judged by the surface moisture alone. It's possible the soil is staying too wet in the interior of the root ball under this schedule, but it's hard to say without unpotting the plant and examining the roots. It's unlikely it needs more frequent watering, but that is an educated guess based on a few unknowns.
The imidacloprid will take time - possibly weeks - to travel up into all of the leaves and stems. This is not a problem, but be aware that there will be this lag time between treatment and any affect on the scale. The advantage is that it will last in the plant's tissues for much longer than a surface treatment of oil or soap. Any scale that feeds during this time will ingest the insecticide and should be killed. Dead scale can stay stuck to the plant for a time, so manually wiping/scraping them off may be necessary to help determine if they are truly being controlled. Dead scale tend to be powdery and dry underneath their protective "turtle shell" covers; live scale will be more gooey. They're tiny, so sometimes this is hard to see.
Thank you, Miri; that is very helpful. Can you suggest a brand name &/or source for the imidacloprid? I googled it and found a 30-pound bag (!); the other results I got were for insecticides, some liquid, which didn't name their ingredients.
You're welcome. We don't have brand recommendations, but there are probably several that contain imidacloprid. The form we have seen most commonly for use in indoor treatments is granular (like a fine cat litter; not liquid) which is scattered on the soil surface and scratched-in a bit, though this is not necessary if too many roots are in the way. Because it is dry, it tends to come in a shaker-type bottle (as opposed to a spray bottle) and can be less full than the size of the package would imply. Several area nurseries/garden centers likely carry it, especially in the smaller 8-oz. size, though those that choose to only stock organic pesticides they may not. Make sure the package label allows for indoor use and/or houseplants; if not stated, it is presumed to be outdoor-only and should not be used.