Peterthecactusguy wrote:at least yours is green. Mine have weird red growths on them. I do not know how that plant grows... I will post pictures. Maybe the red new growths will turn green or something..
And yes it is always a good idea when using chemicals to NOT spray them on plant tissues. Photo-toxicity seems to be a huge problem with the oils like mentioned above. It almost looks bleached.
Yep, been there, done that. When I got my new collection going last June I did an Imidacloprid soil soak just as a preventative. Everything was fine, then 2 months later I thought I saw a few mealies on my Stenocactus multicostatus. I was using an insecticide-miticide-fungicide spray with Neem oil for my Habanero plants. Been working well for the Habs over 5 years, so I thought "well, that should be safe for the Steno". Wrong. The plant started showing orange spots in a few days, it was completely orange in a week, and after some more time went by the Steno was obviously dead -- phototoxicity. Learned my lesson there, and an Imidacloprid systemic is the only thing I'll use on mealies. As to spider mites, I've never had a problem with them, but if I do, I'll never use anything oil-based on cacti. Speaking of...
Ian has stated elsewhere that alcohol is effective. However, he was referring specifically to false spider mites at the time, although I believe it would apply to red spider mites as well. I also believe alcohol will not produce a phototoxic reaction, which would be a plus in spraying for mites. I'm not completey certain about that, though, so I've asked for confirmation about this several times. No response yet, but I'd sure appreciate getting an answer one way or 'tother. By the way, I'd be spraying cacti with alcohol out of direct sunlight. Since it evaporates quickly, I can see where it would have a definite advantage over oils and soaps given their residual effects.
@JeffWhiteDevil -- yes, I'm having fun with my cacti. Doesn't mean that I shouldn't worry a little bit and anticipate problems beforehand. Better that than let those problems get the drop on me as I go "what the f*** do I do now?" With that said, I confine myself to anticipating things that can be reasonably expected.