Is my cactus going to die?

I've had this cactus for almost 20 years. In the past year or two my cactus has come up with either a fungus or some kind of bug infestation. An oval patch about 5" long and 3" wide has kind of either dried out or eaten away at the side of the plant causing a sort of hollowing out of 1/3 of the thickness. The plant otherwise seems healthy and has the same kind of leaf growth in spring as always but if this hollowing out business keeps going on she'll soon topple over. If there is another cactus lover or plant person who can offer some advice before that happens I'd be really grateful. Here's 2 photos of her.
http://img.villagephotos.com/p/2005-9/1073236/cactus.jpg
http://img.villagephotos.com/p/2005-9/1073236/cactus_lg.jpg
SANDY SANDY
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I don't think this will help you very much, but if it were mine I would put a systemic fertilizer/bug killer in the pot (follow directions). The fertilizer will be absorbed by the roots and circulated through the plant. That will take care of any bugs it may have. Then I would ask my extension agent to look at it and make a recommendation. I use Captan on my grapes to prevent fungus, but this might not be fungus.
I lost my cactus after 20 years, but I think it was because it got too big to leave out in the wind during the summer, and it needed the sunshine. With the pot on the floor, it extended to within 6 inches of the ceiling.
Dwayne

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