I have accedently sprayed my prickly pears with roundup and they diddnt blink so i dont think any oil or soap or whatever will harm them. I will spray mine with ortho and again it doesent seem to hurt the plants but to be fair i dont eat mine. I had good luck with releasing ladybugs and spraying the ants that were moving the aphids when they were eating my plants. When i got rid of the afids on the sedums the ants just started eating holes in the prickly pears!!
