I bought a kentia palm some months ago, and during the last week one stem/group of steams is turning out yellow. Also there are some big white stains on the leaves. Some leaves also have small white spots which I can imagine are mealybugs. The leaves with the green stems are still healthy. I live in a cold but humid place (sometime mold problems) and maybe I over-watered the plant, but I am not sure.
The big white stains on the leaves could be a few things
- powdery mildew: unlikely given the hard waxy coat on the leaves. Wipe it off with a damp soapy cloth
- dried salts from overhead watering in the nursery. Were the stains there when you bought it? Wipe it off with a damp soapy cloth with a touch of vinegar and then another wipe off with water
- pesticide residue from the last spray at the residue. Wipe it off with soap and water.
Small white spots
- unlikely to be mealybug as they look like cottony tufts
- possibly scale or boisduval's false scale which is flatter
Get a soft toothbrush or cloth soaked in 5 ml dish soap to 1 litre water and scrape them off.
Die back of one stem:
It's all over for this stem, cut it back to the ground. The other stems can do quite well if you try the following.
- move to an area with bright diffuse light. Even a bright south window with sheer curtains will do.
- water less, this is the cause of most interior plant failure
Kentia palms are the royalty of the palm world due to their tolerance for a wide range of conditions and long life. However this applies to plants that are well rooted. A common situation is to buy a plant that has been shipped from the nursery a little too soon. The roots have not been well established and the change to the low light, low humidity conditions so typical of interior conditions makes them an ideal candidate for root rot.
Let the top inch of soil dry out and then water until it comes out the bottom of the pot. Let dry and water again. Typical watering cycles inside can be every 14 to 18 days.