I have grown two pots of Red Sensation for ten years now. I keep them outdoors year round in my southern climate. They have made several pups over time. Some springs, I divide one and use the pups in other pots, the ground, or as gifts, etc. One pot I am allowing to grow into a multi stemmed plant. It is a very simple job to divide them and I have never had anything but success. I wouldn't say they are the most prolific plant I ever saw, but they do seem to produce pups fairly regularly.

If you keep your plant directly in front of the north window it should do fine. And additional lighting will help keep its coloration in. Misting is importnat, too, a humidifer also..Toni

Hello, did you ever find out an answer? I have the same issue on all 4 of mine. I live in San Luis Obispo

Just guessing by the pictures, any chance this is at the lowest elevation of the property and a lot of water runs off and settles in the area of its roots? I assume they grow wild in parts of your town? Often plant health issues start at the roots. I feel like in their native country, they are only attacked by insects when already weakened...assuming that's even a factor. The ants are probably just opportunistic. Also wonder if the power utility has been cutting it away from their wires? Was that picture taken from a 2nd story window? I saw hundreds if not thousands of Cordylines when I visited the South Island and hardly saw any unhealthy ones at all. I would have been looking for them (unhealthy ones) because I was trying to find the coldest areas where they grow. (for the record, they are wild around Lake Wanaka, they become somewhat uncommon in Alexandra though still found in gardens, and there was only 1 in Ophir but it had a short trunk. Suggesting one of the coldest towns in NZ is still zone 8b at worst. This was corroborated by my discussion with a resident who said it got to -10C "once in a while, but not often". Alas, none of them had seed, anywhere I visited, because birds eat them over the winter. Ranfurly is probably colder than Ophir but I didn't have time to drive there. I saw wild colonies of Phormium further inland...as expected because the plain green form is the hardier plant in Northern Hemisphere gardens. After driving past Alexandra I started to see cold-injured zone 9 Eucs, indicating the transition to a colder climate.)