"For trees in wire baskets, cut and remove wire. Cut away strings & burlap or plastic, exposing root ball. Don't remove soil from ball. If tree is container grown, cut and remove container." - United States Forest Service
"Don't use non-biodegradable strings and other (root ball packing) materials. It is best to remove the string and pull back the burlap. It is wise to remove burlap to examine the roots, or to see if there are roots." - Alex Shigo
"Remove twine, treated burlap, and wire baskets from around the upper part of the root ball after the tree is placed in the planting hole." - Dr. Gary Watson, Morton Arboretum
"Remove wire baskets and all burlap except for the very bottom of the root ball." - Tony Dietz, Urban Forester
"Remove the wire from around the top 8-12" of the root ball. Before removing wire and rope/twine partially backfill to support root ball. If the root ball has broken apart ... it may not be wise to plant it. Fold burlap back from the trunk and the top of the root ball if the root ball is firm and fold it down to be buried when backfilling. If the burlap is sturdy or treated, carefully remove it or at least make large cuts in it. (MK's note: most burlap I've observed is treated and will not decay quickly, meaning that Harris et al. would recommend removal if the root ball is firm). " - Arboriculture, 3rd ed.
"Cut and remove the string and wire from around the trunk and top 1/3 of the root ball." - International Society of Arboriculture (ISA)
"After placing the tree, remove wires or mesh." - National Arbor Day Foundation