Leaves yellowing and white substance on bark of Lavendar Star

[tritonal]

I have a Lavender Star bonsai that's about 3–4 years old. I've had it for about a year now, but during this time, I haven't been able to keep leaves on it. The leaves constantly turn yellow, then brown, and eventually fall off. The lower branches no longer have any leaves at all. When I scratched a bit of the bark, I noticed it's yellowish-green underneath.
The bonsai also has white specks all over it, which I believe is scale. I've physically brushed the tree from top to bottom to remove them and have been using neem oil weekly, but they keep coming back. About a month ago, I removed the top inch or so of soil, but as you can see in the picture, the scale has already started to return.
Should I do a full soil change? I've been using normal tap water and Osmocote Plus as fertilizer. The soil is Tinyroots mix with akadama, red lava rock, and pumice. I've read that this bonsai prefers more acidic soil, so I've been adjusting the pH of the water to around 6.5-7. The first picture shows the bonsai right after I repotted it from a plastic pot.
Since then, I've removed all the wiring because I want to focus on getting the tree healthy before redoing it. It has been growing upper branches and regrowing leaves, and it constantly tries to put out flowers. Lately, I've been pinching off the flowers so the tree can put more energy into leaf growth. Currently, it’s under a Spider Farmer SF-300 grow light, as I wasn’t sure how it would fare outside during the Michigan winter.



to around 6.5-7

 

[Ruddigger]

Those are bugs. Get em off.

 

[tritonal]

Those are bugs. Get em off.

Thats what I thought, but I don't know how to keep them from showing up. I've physically brushed them off, I've used a 50/50 mix of 70% alchohol and water with a toothbrush, I'm using a neem oil spray once a week and I've removed the top inch of soil and replaced it with new. I don't know what else to try.

 

[Orion_metalhead]

Pretty sure Grewia are tropical and would not handle any temps lower than 40degF. I dont have one myself so Id juat focus on basics. I think you may be overthinking it with ph levels and such.

Pests are a normal thing for these type of indoor plants. Just treat with neem or soap spray solution. They come and go. Air movement will help poasibly also.

Yellow leaves are probably due to lack of light. How long is your grow light on daily and how far from the tree is it? Is the getting any natural light?

I expect my tropicals to struggle in winter. I put them outside in spring once danger of frosts is over. If this is an option for you, it will definitely aid in the overall health.

 

[tritonal]

You are right on the overthinking. I have a 120mm fan that gently blows on it during the day while the light is on if thats not enough I can easily add more or keep it running for longer. the light comes on at 6am and off at 9pm and is about 6" or so from the top. I know growing indoors isn't ideal, just making it through to spring. I have a few grow bars I can use as well if it isn't enough. It's also in a window that gets direct sun for a couple of hours in the morning.

 

[Orion_metalhead]

I would leave the light on til 12am. 6am to 12am.

the little fan is fine.

Just deal with the pests and water correctly.

 

[ABCarve]

If you’re using premixed, store bought neem oil, I’ve found that it’s not strong enough and mix my own up from concentrate. Seems to do the trick if you stay on top of it. Once a week. Yellowing leaves are the norm for this time of year.

 

[tritonal]

If you’re using premixed, store bought neem oil, I’ve found that it’s not strong enough and mix my own up from concentrate. Seems to do the trick if you stay on top of it. Once a week. Yellowing leaves are the norm for this time of year.

I've been using a premixed I got on Amazon. I just ordered some 100% neem oil to mix up myself and will give that a try. I've also adjusted the light schedule and will physically brush them off again this weekend.

 

[shohin_branches]

Mealybugs. Every three days remove visible bugs with a cotton swab dipped in rubbing alcohol. Treat with a systemic. Be persistent

 

[Wires_Guy_wires]

For mealybugs / woolly aphids I just skip the neem oil; it slows them down but it doesn't kill them.
Systemics, and thoroughly, is the way.

I say thoroughly because they evolve resistance in two generations. You either kill them right then and there, or they will be back with a vengeance, now resistant to whatever you used in the past.

Check your other houseplants and treat or burn those too.

I'm pretty much against biocides with just two exceptions: scale and mealybugs.
All other things can be overcome with time, mild or even non-toxic means.

 

[tritonal]

Thankfully no other houseplant shows any signs of them. My only other bonsai, a dwarf jade, is showing no signs of pests. Same with my other house plants (mostly porthos). I got some systemics this morning and will treat it today. I'll also whipe it down with cutton swab and alcohol. Once I have the pests under control I'd like to make sure my soil is correct. Currently I am using https://www.amazon.com/dp/B07P6Y6TVW?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1. I was reading that they like a 50% organic mix so not sure if I should add something to it or change it out completely.

 

[ABCarve]

Thankfully no other houseplant shows any signs of them. My only other bonsai, a dwarf jade, is showing no signs of pests. Same with my other house plants (mostly porthos). I got some systemics this morning and will treat it today. I'll also whipe it down with cutton swab and alcohol. Once I have the pests under control I'd like to make sure my soil is correct. Currently I am using https://www.amazon.com/dp/B07P6Y6TVW?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1. I was reading that they like a 50% organic mix so not sure if I should add something to it or change it out completely.

I don’t add any organic to mine, however they are thirsty plants. It depends on how frequently you water and climate. 50% seems a bit of an overkill.