walnut tree

i have a walnut tree that is very big,produces a good crop every year,is in good health,but at the base there is a hole 1x1.5',is there anything i should do to cure this or let nature do it's thing?

 

Just 'let nature do it's thing' - whatever you do, don't try filling the hole with anything.

 

I would suggest you have a qualified someone inspect the cavity. Letting nature take its course is ok but since you say it is at the base of the tree that may mean nature makes the tree fall over. Cavity filling is not suggested any longer as mentioned.