i would pull the tree out and check the roots for rot. if you see brown mushy roots, rinse all the soil off the roots. then sterilize a pair of scissors and trim off the rotten roots. sterilize the scissors afterwards so you don't spread it around.

i've read you could dust with cinnamon, or use a diluted hydrogen peroxide spray or an anti fungal spray for root rot. no personal experience.

if there is root rot, your soil is contaminated and should be thrown away. bleach/wash your barrel and let it sit in full sun for a few days. or throw it away and get a new pot.

use a well draining medium. you could use Al's mix, or use a store bought mix, but add extra perlite to it.

June: I am sorry to hear of this. I hope what Houston has said helps you.

Good luck

Mike

Thank you for the suggestions/comments, everyone.

It appears there is NO root rot and the roots actually smelled earthy and healthy. They looked normal too.

For now, my husband drilled a few holes into the bottom of the whisky barrel and we have it on a new barrel mover (the other cheap one broke) and the water is draining. We also added some new soil and hope he perks up soon.