Help please - can I rescue this... ?

[parakeet]

This cactus used to look entirely different a week ago. A lot chunkier and healthier.

I've been noticing tiny flies around my house for some weeks (upstairs, downstairs). I figured it may be related to a dodgy spider plant elsewhere in the house.

But I noticed today that the tip had shrivelled up. On closer inspection, I saw that the flies were congregating on around the cactus (tapping it revealed a couple more).

Also of concern - prodding the cactus reveals it to be rather flimsy; feels hollowed out inside somewhat.

Is there any way to turn this around?! I'm beside myself, because I inherited this from a late friend.

On my father's advice, I filled a squirty bottle with water and some washing up liquid and sprayed the plant with that. In his experience, that's killed blackfly on leaves.

Happened so quick. Though the flies have been around for a while, it was only today I noticed the change in the plant.

[lordarutha]

I am by no means an expert but looking at that poor plant it seems it is most likely beyond help. The black flies are probably fungus gnats and they really shouldn't have done that much harm to a plant of that size, it looks like it has rot which is more likely due to over-watering. The only thing you might try is to take it out of the pot and remove all the soil. If you do find it still has some roots Re-pot in a gritty mix and dont water it for at least two weeks, then give a little water sparingly but alow it to dry out between watering. If it is winter where you are leave it dry for the rest of the winter.

[iann]

Throw it away and get a new one. There is a (very) faint hope that you could keep this plant alive but it will never be happy. With the next one, use a much grittier soil, much less water, and much more sun. The pointy bit on top is not natural, it is caused by being grown in the dark.

It appears to be a Ferocactus, hard to be sure.

[hegar]

Both Ian and Paul are right. Your cactus does look to be on its way out. It most likely is totally rotten on the inside and only some of the areoles from which the spines arise are still green. Sometimes you can save the top if the rot has not yet penetrated it, but a lot of the time this is still an effort in futility. When you toss out the cactus you should either heat treat the growing medium (soil) or discard it. Also, if you are going to reuse the pot, it too should be sanitized (sterilized). A chlorine solution (three parts water to one part clorox) will take care of any fungus that might be present and could infect the new (replacement) plant.

Harald