Repeat offender, Opuntia?

[volvogrrl]

Happy summer everyone! I have here what I believe is an opuntia with a repeating problem. I rescued it from a hoarded house, and the base of the plant is a collapsed pad from a previous near-death experience. Since I have had it, lavished it with lots of TLC, it has managed to grow two new pads over the years. Each one started out fat, healthy and green. But then all of a sudden, they would get black patches, and fail to grow any further. When the second one started I hoped all would be well, but now it is starting to do the same thing. Is this sunburn? Pests? There are a couple house spiders that live on the plant, could they be the culprit? I would really like to see this cactus do well. Got any suggestions?

[Aiko]

Black spots usually is a result of frost. But I guess that does not happen in your location at this time of the year, even at night?

[volvogrrl]

It didn't freeze this year, and its about 60 degrees at night right now.

[globose]

Maybe a fungus or bacterial infection from that deteriorating base? are they soft or do they have any kind of odor? You could try too get a cutting from the healthier looking pad

[volvogrrl]

The collapsed base is firm and doesn't give to any pressure. The new pads are a normal firmness, and the black patches are the same consistency. If it grows a new pad I will remove it right away to try and grow and entirely new plant. Thanks for the tip!

[greenknight]

There are a couple species of fungi that cause dry rot - black patches that are firm, like your plant has. Nice little discussion of this at Black Spots on Cactus | Home Guides | SF Gate.

Their direction for rooting cuttings are wrong, though - to root an Opuntia pad, just lay it on the surface of the medium, which should not be wet.

[Charles]

Cacti disease or wasps? I took a few photos of a "disease" that struck my cactus garden these past few weeks. I also bought an electron microscope. Will try it tomorrow.
I thought at first that it was slugs, but have not seen one in my garden for 10 years. Then, I thought it was a fungus. Its still warm here so it is not Frost damage. The roots look okay too.
Yesterday, I saw a wasp that appeared to nibble on a cactus stem. If the wasps have learned to eat cactus membranes, then I'm in trouble. My garden has zillions of pee ants but the only eat the cactus pods.
Here are some photos of a Cholla, a pencil cactus and an Opuntia with the affliction. The last photo is an Echin. being treated after a bath of water, B-1, fungicide, insecticide and rooting hormone, and left to dry in garden lime before pot planting.
(does anyone have four thirds macro lens?)
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