This is a huge Cereus hildemanianus sub. uruguayanus with several of these spots on it. One of the photos show dried holes thru the plant. There are small sections like this active spot that have been carved out and left to dry and they are doing fine. Should I cut these infestations out? And maybe smother the sut area with sulfer powder? Any help is appreciated. Thanks, Xuling
I suspect it might be scale. If so, I would use a systemic on it. I am totally orgainic except for scale on cacti. When I water a plant with a systemic, I get fresh dirt to cover where I watered so other creatures don't touch the wet soil. One treatment seems to do the trick.
Where do you get such stuff Baja? I have never heard if it, but then I am still a virgin also. I have cull it all out and sprinkled the surgical sites with sulpher. Don't know if that is right or wrong or indifferent. Xuling
There are several sources for imidacloprid. You can see a few of them if you google into the different brands.
The product in the photo is a lower strength version of another Bayer product, which should work fine too. Typically I put 0.5 oz into a liter of water. That's probably on the low side but I'd rather it be that way. Then I drench the roots with that. You have to be careful to shake really well right before pouring it out because it tends to settle to the bottom otherwise. And don't treat plants with a systemic when the soil is bone dry. Better that it be slightly moist so the roots are active and able to absorb the active ingredient. For a plant in the ground, maybe 36 hours after a good watering. I'm sure other people have different ways to do this, I'm just relating what has worked in my experience.
I'm not sure if scale is your problem, Xuling. This is just in reply to the question about how to handle a scale problem. You sure that's not just frost damage? Scale does not eat away at the innards, it stays strictly on the skin.
What ate the holes in the arms is probably different that the photos I posted. Anyway as I said they are cut out and the cut sprinkled with sulpher. I do not believe that the areas are a product of the cold. That plant can take it quite cold. X