Question
my Saguaro is oozing black tar like substance

Answer
Dear Mary,

That's not good.  It usually indicates rot.  What part of the plant is it oozing from?  I ask for two reasons: 1. depending on where it is oozing, at least in part it be saved and  2.If it's low and bad enough it can fall and really cause a lot of destruction if in the way of anything, including people. A 20 ft. saguaro weighs about 16,000 lbs!

If you have a picture, that would be ideal. But height, area of rot, whether or not it has arms,  and if it listing are all important questions to answer and then I can help you more. If it is listing  from the base you need to do something immediately, because even though it's listing in one direction it can fall in another. In that case you have to get a certified cactus horticulturist.  The Arizona Dept. of Agriculture can point you in the right direction.

Hopefully that's not the case.

My prejudice is to save a saguaro if at all possible, they are protected and rare.

Look forward to hearing from you.

Maureen