Question
i have a globe willow that has white mold growing in the cracked trunk near the bottom of the tree the bark is dead and pealing?????   help i don't want it to die what should i do ???

Answer
Sounds like a decay fungus fruiting body--like the flower of a plant. One of the life stages of the fungi is producing a conk or mushroom type fruiting body. Decay fungi enter the tree through a wound in the bark and slowly eat away at the woody cells. They do not harm the living cells just under the bark. As the fungi grows it will hollow out the tree trunk and even hollow out limbs as the fungi moves up the tree trunk. Tree can live many many years as hollow trees. IF the hollow gets into the limbs the limb could break off during a storm.
The woody cells are dead cells and not associated with the healthy of the tree except for strength.
Trees can and do live many many years with their trunks completely hollow. Trees have the capability to seal off the decay fungi and slow the growth of the decay. IF the large limbs start to break off and the end near the trunk is decayed or hollow then the tree may have reached a point that it could be a hazard. And then it is only a hazard if it is locates near a structure that could be hit by a falling limb. Yours sounds a long way from that stage.

Some hollow trees may have so little healthy tissue surrounding the hollow area that they must be regarded as dangerous, but this is by no means the norm.  Trees do not become hollow overnight - it can take decades - and while the center of the tree (the heartwood) may be decaying, the tree continues to lay down healthy wood (sapwood) around the outside of its trunk.  This results in the formation of a cylinder, the strength of which depends upon the percentage of healthy to unhealthy tissue.

The first sign of the tree being a danger is large limbs breaking off and these are hollow. This means the decay has reach the limbs and is fairly extensive.  
There is not any treatment that can remove the decay and you really would not want to do that anyway. The best thing is to keep the tree healthy by fertilizing it with 10-10-10 fertilizer at the rate of 1 lb of fertilizer per inch of trunk diameter scattered around the tree and watered in good. Apply just before a rain storm and you will not need to water it in. Do not worry about the fruiting bodies they have no health problem for the tree.