Ben wrote:

Hi,

I have a small cactus display, with about 4 cactuses in a bowl, surrounded
by some gravel. One of the cactuses is similar to a prickly pear cactus,
only it has very small 'furry' spines rather than big sharp ones. Its about
9" high, with 4 'pads' on top of each other. Anyway its been growing really
well, 2 new pads had started to grow out of the top one, and it looked
healthy. But for some reason, recently the bottom pad started to rot, it got
very soft and squidgy and the cactus started to fall over. I tried
supporting it, and making sure the soil was dry to stop the rot, but alas
today, it fell, the bottom pad is just squishy mush.

Too much water at the roots. It is almost impossible to kill a cactus by
neglect but all too easy in winter to get them by wet rot or frost
damage. Some opuntias are frost hardy but not O. microdasys.

My question: Is there any hope for the rest of the cactus? Its all looks
healthy enough. Can I put some rooting hormone on the bottom pad? Will it
take?

The bottom pad is probably long gone if it has flopped over. The
adjacent pads may well also be infected. Rooting hormone contains a
fungicide that might help a bit, but you need to cut off the good pads
ASAP and leave them 24 hours to callous then plant in a slightly damp
sand/grit mixture. If you are lucky they will grow again.

If you don't cut the rot out ruthlessly they will definitely die.

Regards,
Martin Brown