Before I use the Bayer

[Rooney12]

This beautiful old cactus came to me in April as a wedding gift. I'm told it could be 9-10yrs old, so I surely don't want to let any death happen on my watch. I don't know a whole lot about cactus care, but I put him in my sunniest corner and gave about 5cups of water once in late May. One of the three branches came with some battle scars (closeups in the photos) which are not soft at all but very woody like tree bark. This branch actually produced a little bud in early May, which I was very excited about but it slowly turned black and fell off. That worried me and prompted the watering. Just last week I noticed the whole branch was covered (like, covered) in little beige lumps. From these forums I got the impression it might be soft scale? They came off with even a light fingernail scrape, and have a paper-y consistency, like sawdust. I washed the whole branch with a toothbrush and some soapy water, and got most but not all of it off. The flesh underneath is now much more yellow-green than the other two branches. I can see signs that it is spreading to the bases of at least one of the other two branches. I've gotten myself some Bayer Advanced Tree and Shrub, since that seems to come up a lot. Before I just launch into an attack, can anyone give advice on how to administer the poison? Should I give the cactus a soak at the same time or would that make things worse? Any other ideas to course correct my shoddy parenting?

Much Appreciated!

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[greenknight]

The manufacturer says not to spray it on the plant, pour it around the base of the plant. Follow their instructions.

[hegar]

I assume, that you bought some Bayer Tree and Shrub systemic insecticide, which contains the active chemical imidacloprid. Of course, if what you do have are armored scale insects, most likely the one called Diaspis echinocacti, and the insect has not yet developed resistance to the chemical, treating the water you apply to the plant with the Bayer chemical should take care of the problem. The systemic insecticide is designed to be taken up by the plant's root system and then moved up into basically every cell of the cactus. I do not think, that actually letting the water-insecticide mixture running down the stem would hurt the plant. However, it would be a good idea to look, if the insecticide can also be applied to a plant's stem and leaves. With a decent hand lens, having a magnification of 10x or better, you should also be able to figure out, if your problem is indeed a scale infestation. Using a needle, you could lift off the roundish cover carefully. If it is a scale, you will see a small, soft insect body where the cover was removed. Bayer's chemical would do you no good, unless you are treating an insect infestation. If this were a disease, the treatment would be a waste of your time and resources.

Harald