Question
Each year, my pear cacti are beset with white spots that eventually kill the plants. I've asked people what I could do to get rid of them, but one person says it's a bug I have to use insecticide on, while another says it's a fungus that I have to kill with a Bordeaux mix. Can you advise me? I live in central Arizona.

Answer

Cochineal eradication Dear Barry,

I added a picture and you can see if it looks anything like this.  If so, what you have is an insect infestation caused by cochineal mealybugs.

When you see that your prickly pear has white sticky mounds covering it, it means you have a cochineal (mealybug) problem. This is not a disease, it is actually an insect infestation. The white sticky mounds are the housing for cochineal bugs (also known as mealy bugs). When these white sticky spots first start to appear it is best to spray them off the cactus pads with a power nozzle attached at the end of your hose. If the infestation begins to get out of control, I suggest treating the areas by scrubbing them with insecticidal soap or unscented dish soap. In small areas you can scrub with a tooth brush but for larger areas it is best to use a long handled brush. Or you can just spray all of the surfaces of the prickly pear pads thoroughly using a power nozzle attached to your hose and then thoroughly spray with a solution of spectracide and insecticidal soap. Do not rinse after applying the spectraside and insecticidal soap.

During the winter months the most effective method of cochineal eradication (getting rid of the white sticky spots on your cactus) is to spray them with Neem Oil spray which can be purchased online. Follow the Neem Oil manufacture's directions. I prefer this method of eradication because no scrubbing is required in order to kill the cochineal insects.

If you prefer an organic treatment, power wash your prickly pear pads using a power nozzle attached to your hose and then use an organic natural soap and neem oil solution to spray, then scrape with a brush and spray again with the solution and do not rinse. This will remove the cochineal scale and mealybugs organically.

If this is happening again and again, I suspect your plants are in soil that is infected by mealybugs as most live in the soil.  If possible I would either start clean pads in another part of your yard or take you cleaned plants and move them, checking the roots for the bugs.  I favor the first as I can then let the soil rest and also treat it to get rid of the cause.  With nothing to grow on they will die.

What is a Bordeaus mix?

If you have al lot of big plants you can also have this done professionally as it's not a fun job.

Let me know if this is what you think you have,