The blue is not fungus, its residue from fungicide thats been used before you bought the plant. Many fungicides leave a blue or white powdery residue. Nothing to worry about other than that it's toxic if it gets ingested, licked by cats.... In production they keep them very humid and will use fungicides to keep the leaves in pristine shape for sale as the tips often go brown. They should use a mild detergent to clean them for sale. Cordylines also often shed lower leaves when placed in a new environment especially a much drier one. This is also not something to worry about, though you could improve humidity one way or the other. Look at the roots if they are nice and white thus healthy it's not a root problem. Root or stem rot will cause the lower leaves to drop off very quickly. It's unlikely this is your problem indoors though. Older leaves will look spotty and brown parched, before they abort, also no problem. However the large "water mark" in the healthy pink leaf is symptomatic of something, probably dry air in your case or possibly over watering, no drainage at the roots, or even lack of water at the roots, check all these things. It could also be burnt from being too close to a window or a lamp. To increase humidity sit the pot on some pebbles in water don't over water instead. They do like a moist soil but not a boggy one. Indoors they also want the brightest light possible short of actual sun, certainly in summer as the leaves can scorch through glass. The leaves are thin in most cases and burn easily or dry out easily especially the new leaves. Also don't feed more than just a tiny amount once a year indoors. Cordylines quite frankly don't make the best house or office plants because they love humidity and warmth so much and because the leaves are most often quite thin. To recreate ideal conditions would make anyone using the room uncomfortably steamy. However if your climate is good you can place them outside for a few months (even just summer) then inside for one, rotating them as you go, or just inside for winter. Other wise look for the varieties with the thickest leaves to try, there are one or two that with some help should do better as a result. Off hand C. fruticosa "Vanuatu" is one, shiny largish jet black leaves, arranged beautifully. I've never had any problems with it's leaves outdoors in full sun and drenching rain, humidity and a dry warm winter. Some of the rounder paddle shaped small ones or the larger leaved reds with the same thick leathery leaves might also do. Dracaena are all round are far better than Cordyline fruticosa for permanent indoor use. You are unlikely anyway to get a fungus problem on the foliage indoors only possibly at the roots or the cane. Fungicide could help with that but then it must be mushy wet and black to be that. Lower older leaves don't always look their best indoors but it is technically better to wait for them to drop off rather than cutting them off or the plants stem (cane) might get thinner and thinner in the process, bending over and ultimately die. Hope they've survived meantime anyway!

Ciedyline is not an annual. I successfully overwintered mine for several years. After it “trunked,” I tried following the advice of dear Campanula, to score the trunk to stimulate growth lower down. It died soon after.

if dead.. things rot .. and eventually it can be easily pulled out.. whats your hurry No "hurry", per se, other than the aesthetics of it this or next year. I liked the look of the mandevilla with it, but I don't have any this year so I probably won't do that again until next year. I was also concerned that the roots of the mandevilla could be wrapped around the roots of the cordyline, and its rotting could lead to killing the other. If that's not an issue, though, then I'll just cut the old stalk down and let it do its thing :-)

Not enough information to diagnose what afflicts the plant. How long have you had the plant? On average, how long between waterings? When you water, are you making sure the entire soil mass is soaked? Have you fertilized it? If yes, describe what you used and how you went about it. Flushing the soil when you water and allowing the medium to dry down to nearly dry will fix the mineral deposits on the soil's surface - no need to repot. It's best to use a 'tell' to 'tell you when it's time to water. Proper moisture management is an essential part of keeping your plants at a high level of vitality. Using a 'tell' Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant. Watering in small sips leads to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor. In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water. Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'. One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue. Al