Remove the mushy root to heathy tissue and clean cutters after doing this. Might be a good idea to check the crown to make sure it's not decayed inside. Wash hands to keep from spreading root rot to any other plants. Just in case thats what it is.

How mushy is your "mushy"?

Rhubarb roots, at least the central part, are very pithy/spongy in my experience. As long as you are not seeing slimy-gooey mushiness, you should be fine.

on many plants.. and mind you i have NO experience with rhubarb ...

you could throw the root in 10% bleach.. for 10 mins or so.. to bleach out any rot ... [it is done with hosta all the time]

perhaps others will advise ...

now.. that said ... with the heat of summer coming.. i may have waited until fall.. to dig .. if that option was available ... though i do fully understand.. you have to strike when the offer is hot ...

i might pot it up for TLC.. until fall planting ... though i have no clue.. what media i would use ... throw it in full bright shade.. and keep on the dry side ... a lot of these tuber like root plants.. dont like a lot of water ... think about storing potatoes in the house ....

ken

I would NOT put a spongy root like a Rhubarb in any bleach solution...

Hosta roots are very different.

I often use smell and color in this type of situation. If it doesn't smell like it's rotting and the color doesn't look like it's rotting, I'd leave it as is. When rhubarb rots, it turns a slimy baby poop brown.