Verticillium wilt is very present in PNW soils......it is a pretty common problem and seems to affect Japanese maples more so than most other species. To answer your questions.....you can have it tested and confirmed if you wish but it is not absolutely necessary if you are feeling relatively secure in your diagnosis. The second tree may not be infected. VW is an opportunistic pathogen and typically infects trees that are stressed or damaged for some reason. It is quite possible to have a second JM or other susceptible species close by that is untouched and often will remain so. Species that are not as prone to VW as Japanese maples and older, very well-established trees can often survive the disease long term with only partial dieback, provided proper care is given. I have yet to see a JM infected with VW in our area survive very long, so forget the 'management" approach. It just doesn't work with a Japanese maple :-) Typically, VW is extremely fast acting with Japanese maples, with the entire tree dying in a matter of days. It will not hurt at this point to take a wait and see approach with the affected tree - significant dieback that is present in spring (by failure to leaf out) may or may not indicate imminent death. Usually, VW and the very rapid decline shows up in mid to late summer, but with the extremes our weather has demonstrated over the past couple of years, these early season signs of the disease are becoming more prevalent. If the disease is confirmed, the tree should be removed, but I'd be extremely careful about root removal. If there is any chance the roots of the problem tree have intermingled with the nearby healthy (so far) tree, leave them alone and in place. Again, VW is present in most NW soils so it is very likely the pathogen is throughout your garden. But it is typically present in an inactive or dormant state unless stimulated into activity by root damage, mechanical damage or excessive stress. If planted carefully, given proper care and good garden sanitation adhered to, there is no certainty any other susceptible tree or shrub on your property will contract the disease. In my old garden, I lost two trees to VW, one in the front and one in the backyard. Since they were never present in the garden during the same time period, there was no chance one could have infected the other. VW susceptible species were planted close to both but were never infected either. But I never disturbed the root systems - the one in front (a JM) I cut down and the young western redbud in back I just left in place as a vine support until it finally rotted away. It is disturbing to lose a valuable and well-loved tree to this disease. But it did not discourage me from adding additional VW susceptible plants to my garden, however any new Japanese maples I did confine to containers to reduce any further possibility of problems. That became the start of a rather large collection of containered JM's, which I was able to take with me when I moved. Wouldn't have been able to do that had they been planted in the ground, so there's a bit of a silver lining in any dark cloud :-)

Combo root system not yet well established plus hot and/or sunny weather. Not a disease. Treatment: regularly water the root zone.

Looks like a combination of bugs eating leaves, sun exposure, and too much grass. Gently pull up the grass and pit down mulch. It is the end of the summer so the tree is getting ready to go dormant. No point in spraying for bugs now. Next spring pounce if u see the japanese beetles. How much sun does the tree get? how was the summer, wet or dry?

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