of fungus gnats being present? Seeing them fly around of course is obvious. What are the others
that have been observed?

white specks crawling on the soil when disterbed.   use water and handsoap 1/3 soap 2/3 water water the soil after a few weeks they will be gone.....let the soil dry some to prevent returne.

i did not notice any flying kind, I saw my Desert King that had 4 sets of leaves totally wilting and I could not figure it out..so I looked under the magnifying lense and saw the little fast ant like black fruit fly creatures.. running all over the soil... I could not see them without the magnifying lense... I took the cup outside and opened it immediately to see if I could transplant to another pot..but there was no roots, no bark and nothing left, it was one of those 1" wide cutting, it was laced with tiny holes all over. I never saw the larvae.. I assume it is microscopic...for this old lady's eyes to see.... but they are bad!   Knowing that, I sprayed all my pots and I finish killing some of the semiliving ones.. it was pretty awful... with more cuttings ready for cups... I poured cinnamon all over and stop giving them anywater... they almost dried out of thirst and I keep repotting and zap the soil in the microwave...I don't think they can survive that.   Well, not sure where I got it from, mas now that I know, I look at them every time I have a chance. Again, I did not see any flying kind...these are soil living creatures. don't wish them on anyone.

the hand soap kills eggs and larva or messes with thier reproductive cycle. somthing to that effect. i have seen flying things like fruit flies and white specks in the soil moving about. as soon as i see that its to the handsoap mix. i only get them when growing indoors, never outside.

the hand soap does not harm the plants?

nope not at all. i use soft soap myself. dish soap might hurt the plants though.

been using soft soap for year for indoor plants. and this little problem

Mike, typically you spot them visually running around on the soil surface in your pot. You sometimes see them flying if you have a bunch & the back lighting is right. They are small. It takes very few larvae to get what Grasa describes, no roots or severely eaten root systems. There is an recent thread describing possible solutions including mites, soil bacteria & Bounce fabric softener sheets. There is scientific research supporting all those approaches. I have seen claims from people claiming that diatomaceous earth will control fungus gnats but there is a number of scientific publications disputing that.

I  am skeptical about Dave's hand soap suggestion. It is the first time I've heard of it, but I would anticipate that a concentration of detergent (hand soap) high enough to be toxic to the fungus gnats would also be toxic to the plant. Possibly he has done this with hardy plants and, since they lived, did not notice toxicity. Possibly he uses less soap than I understand from above and the hand soap he uses contains another chemical that has specific toxicity for the gnats.

Good luck with your trees!