Overall decline of the entire patch... I am looking for the least toxic approach here.

I don't know much. But my mother had a fungal and bug problem on her cactus like this one and she mixed dawn dish soap with water and scubbed it carefully with an old broom. Cactus is starting to look a lot better now.

Anything you do now is going to affect the blooms. Those small flys are waiting for the flowers to open. Also don't know about the weather they have been thru. Like hail or heavy rains. Give them a chance they may pick up with extra sun and heat. Just my guess not knowing all the facts.
Stush

Dawn soap is an amazing thing. I hunt bugs on my cactus with it. Those bugs there are fast movers. Coreid bugs are another one that I don't see here but could be what has been leaving the marks. They leave hickies everywhere. My big old Mexico was dripping white schizz. It was bad. I cut about a hundred pounds of ugly pads off and sprayed with soapy mixture, and it grew back within a year. I hunt for bugs pretty routinely. There are fewer bugs now but it is a thing one needs to keep onto. Where are you located California, Texas Southeast? These bugs are more prevalent in the southeast and Texas. I do not here westerners complaining about them as much. I think bugs come with the humidity. Hopefully you do not have the Cactoblastis cactorum, a opuntia eating (an killing) moth (the larvae that is) that is now in Florida. I have not seen it in Texas yet.

I mix my ORIGINAL Dawn in a spray bottle so it is about half the darkness of windex. It is still sudsy when I spray. That gets into the bugs breathing apparatus and then you can watch them die pretty quickly.

I was considering the insecticidal soap route. It's a "spineless" variety. I wonder if it's less resistant to insect attack. The landscaping company that "maintains" the park seems to mow and radically over trim the trees. Not sure we want them diagnosing plant illness.

We are in Texas. I have a spider mite battle in my own yard...hopefully the recent rain has knocked those back a little. Time for midnight gardening - insecticidal soap edition.

God bless YOUR little heart, thank YOU for trying to help these local cacti

The important thing with these bugs is the sudsiness of your suds.

Mara,
Your right. We don't suffer that problem up north. Our winters must keep them checked. I know when first planted they look so nice but when they get old, they do look sickly. Some times you have to start over and replant. But up here is different then down there.
Stush

Stush,

I always said the better the growing conditions, the better the threat to Las Plantas Notras. You should see the size and quality of mealy bugs and scale available in Southern California.

Like I said above, a major butchering coupled by routine bug hunting on the remaining stubs will get things get a nice restart, and one will be back with a good looking plant very quickly.

We get cochineal bugs here but not a whole bunch of mealies outdoors.