[Cynthia, Prescott, AZ]

I would use Bayer Advance Tree & Shrub at 2 T per gal. I have seen it recommended at 1 t per gal, and this may work too. I just did my entire GH with close to the 2T per gal, so will report later on the effects if bad. You want to use the concentrate, because you will be using a lot to soak the pot and the mix, the most effective way to get at the mealies living in the mix and sucking on the roots, if an open mix like bark. B A Rose & Flower ready mix is too expensive, and has a synthetic pyrethrin in it that some orchids don't like.

Crown rot is not root rot. If the innner most leaf is not rotted down to it base in the plant, you do not have crown rot, and things should be easier to deal with. If you have any live roots, a repot with these just under the mix, but near the surface, so they are dryer than normal, should work.

Physan 20 is not systemic, and will not penitrate any part of the plant to kill rot, but will clean up the exterior to a great degree to avoid further rotting. It must be used carfully, as an over dose is very bad for the plant, and a lowered concentration may be better. Phyton 27 is a systemic fungicide/bacteriocide, and is well worth having around and used sparingly, as it is very expensive.

If you repot and find some live roots in the pot as well as the living airial roots, I would not remove the spike, if there are at least 2 or 3 good and large leaves. These can handle the spike. Many fungicides are very specific to particular fungi, and may not hit your particular fungus. Don't know about mixing the physan with BA products, but I would consider the BA products more important. A good watering schedule will take care of further root rot.

A certain number of dead roots in a pot are normal, at least for me, as I believe there is a limited life span of the roots.