Sounds like aphids alright. Insectidal soap is a very effective treatment for aphids and non-toxic. I've used it on my Japanese maples many times to control aphids. Make sure you mix it properly because the soap can damage new growth on JMs if mixed too strong (I found out the hard way). You probably will have to reapply the soap several times at weekly intervals to fully control. Ladybugs are another good organic control measure.

Japanese maples are disease susceptible and sensitive to impeded drainage. They are also woodland trees that may be damaged by hot sun in summer. If you look around a bit you will see there have been multiple others with Japanese maples that are dying back etc. Some stock may be coming from nurseries already infested, due to apparently careless propagation and production practices.

get out the scissors ... and snip them off.. wrap them in plastic.. burn the lot.. and bag the ashes.. and drive them 60 miles from the house ... and be done with them .. the tree is gorgeous.. and way under-potted.. either get it in mother earth.. or put it in a bigger pot until the next proper planting time.. since it is most likely severely root bound.. i would probably recommend some severe root pruning.. but again.. i would do that when it is dormant.. which is the next proper planting time ... ask in the tree forum if you want some further info in that regard ... ken

There is not a single topic where qualified horticultural professionals do not have dissenting opinions. Indeed, over time, yesterday's crackpot theory becomes today's widely accepted practice. Andvthe reverse is equally true. I can provide examples of each. I have no problems with disagreement...it means we have views that are different, nothing more. I can tell you this much...technically, no diagnosis should be given without a lab report. In practical terms, symptoms are given, probable diagnosis are given, no lab ever consulted. Same with nutrient issues. Very few are going to go through the trouble of collecting samples, sending them in, and waiting...and nearly every soil test i've ever seen has at least a token amount of fertilizer recommended. And who exactly is going going to go for a tissue analysis? Except in extraordinary circumstances? So making this claim is misleading, it's an attempt to shut down dissent, not create a conversation. Let's not even start going down the rabbit hole of analyzing and interpreting soil test results...basically, that's one subject where there is no agreement. I'll admit most people fertilize where they have no business doing so. I won't comment on some of the products out there or the claims made by various parties. In particular instance...we have a plant recently acquired, still in a pot. Trying to exclude container practices while claiming the umbrella of established landscape plantings is misleading. For the record, i'm not suggesting we fertilize this puppy till there is no fertilizer left on the county. I'm suggesting a half rate dose of a liquid soluble, aka, a shot in the arm. It can do little harm...and can have the benefit of pushing new growth. Explaing how photosynthesis occurs...great...now, how do plants take up nutrients? There needs to be room for dissenting views, in many forums of life. I'm not promulgating crazy high doses, or mix your own concoctions because i took a high school chemistry class...this is not a radical proposal i'm making. And frankly, it's one respected horticultural professionals across the country give routinely. Feel free to disagree...you can be a qualified and respected professional and disagree. Especially in horticulture.