This Summer I bought a Japanese Maple sapling to make into a bonsai. This is my first one, so I'm very inexperienced. I've determined my problem with it currently is likely spider mites. It is currently losing leaves, which is what I'm assuming it normally does this time of year. So my question is what is an optimum treatment for spider mites during this time of year? Will they die off on their own? And how can I prevent/reduce the chances of my tree from getting them again?

Yes, the tree(and spidermites) is preparing itself for winter. You will not have problem for a while. It is not really sure that they want your tree in the spring. Spidermites are all around and prey on the weakest plants awailable. With good care it is less likelly to get problem.

I have had good success with predatory mites Phytoseiulus persimilis. So if they come back, be prepared to order.

Br
Magnus

Hm.. I do not think I have seen spider mites on Japanese maples before. Normally they should be fairly resistent to this. Where / how are you keeping this plant? Do you keep it really sheltered maybe?

Leaf drop is normal this time of year. (Naturally, assuming you keep the tree outside)

If you are really sure they are spidermites, I spray with insecticidal soap once a week and also try to keep the foliage with plenty of humidity.

@Clico Thanks! I'll definitely do that if they pop back up this spring.
@leatherback I'm a pretty big newbie, and had just repotted/ damaged some of the roots a couple of weeks after purchase and in addition, it was being pretty munched on before I had moved it to the atrium. It's still exposed to the sky/air/rain but it has walls on all four sides and fewer plants around.
@Tropfrog Beneficial insects might be a problem given I'd have to bring them through the house where my very skittish family lives. (it's currently in an enclosure that while is technically outdoors, is only accessable by going through the house) They dislike bugs. A lot. (and to a lesser extent so do I. )
Y'all have been great! Thanks for the help!
I'll definitely be using these forums more c:

Heckin Wes wrote: @Tropfrog Beneficial insects might be a problem given I'd have to bring them through the house where my very skittish family lives. (it's currently in an enclosure that while is technically outdoors, is only accessable by going through the house) They dislike bugs. A lot. (and to a lesser extent so do I. )
I'll definitely be using these forums more c:

Well, I dislike poisons, which other people would consume without doubt. Lets just say that we are all different. The predatory mites is in a sealed container on a grey substrate and not visible to the naked eye. You dont see any thing else than improvement of the tree. There are for sure more small critters in your bed, than the amountpredatory mites that will find its way into your home from the trees (and they die imedantly).

Just saying....

BR
Magnus

If you keep your trees in a space like this, you might find you will keep having similar issues. Lack of air movement can affect plants significantly.

@leatherback I was not aware of this. Thank you for the extra advice! I was definitely planning on moving it back out to the backyard after it recovered, but earlier it was getting munched on by a load of things. I'll have to look into some deterrent to chewers, but I do believe I'll be moving it back to a more aired out place.

@Tropfrog I don't feel like getting into the benefits of GMOs and the drawbacks on the sustainability of "organic" farming practices here. (Although I will tell you that "organic" is a weird term to use, as any living thing on earth can be classified as such, but not non-living things. But somehow "organic" salt?)
I have taken a sustainable horticulture class and am going to be taking the most effective approaches that are the least impactful to the environment as possible. I know to use pesticides only as needed, and never broad-spectrum pesticides. These also aren't going to go out into gardens or the like. These will be staying in pots, with the excess water being sent to our drains that lead to water treatment, not stormdrains as well.

Does anyone have experience using such sprays for their trees? Is it dangerous for them? I've read that some of them are plant-friendly so there shouldn't be any risk.

Hey still c, some nutters will tell you that you shouldn't use any pesticides. Don't listen to them. If you buy a pesticide that is for the specific pest you should be fine. If it's meant for use on plants to prevent bugs, you're good for the most part. They use things that kill insects (insecticides) not plants (herbicides). Collectively they are known as pesticides, but they are distinct. If you can identify the specific bug that's causing you issues and use a method to target that specifically (like releasing ladybugs if you have aphids, or using a insecticide that targets the specific bug) it'll make sure any beneficial insects should be fine. Hope that helps!