scale is a plague on them ... try google ... some have suggested cutting them to the ground and then treating it so that the new growth can come out clean ... personally i got rid of all mine for just such reason ... there was a post on this in the last week, if not here, on the garden clinic forum ... good luck ken

Wow lots of interesting stuff here! I think there are multiple issues here, and, since the health of the plants isn't great, I would deal with all possible problems rather than hunt down one specific one. If it were me I would do the following, since doing them would fix any of the most likely problems that you may be having. I would change the mix to a free draining one. I would check the roots, and pot into a container that is only a little larger than the rootball. I would put them in a partially sunny position after the repot until they get used to their new mix and pot. I would then move to a sunny location once things started to settle. I would make sure the room had plenty of humidity with gravel trays or a humidity. I would make sure the room was warm, and provide bottom heat to the pots if possible. I would inspect for bugs. Mites and scale seem the most prolific - possibly mites in your case. Webbing is a telltale sign, and sometimes hard to spot, but not always present. I would treat with Toni's spray regardless (she can tell you the ingredients, or you can search previous posts.) If you do spot bugs, use Toni's spray or a suitable one for fruiting plants from a garden centre. I would water these (after the repot) only when the new medium was closer to dry than damp. In a new medium you won't have to worry so much over watering - if it is the right medium it is unlikely you will overwater unless you go nuts with it. Fertilize only very lightly until the tree is back to health, then feed with a high nitrogen feed every couple of weeks. Citrus bounce back, but they take time. These are not by any means the be all and end all of things you should do, they are merely what I personally would do :) Danny

Could be a fungus like Vladimir said, could also be an insect egg or just dirt on a bit of fluff. However, I'm more concerned with how dusty the leaves are. I may just be dust or it could be the beginnings of a spider mite infestation. It's a good idea to wash off the leaves from time to time, like maybe every 4-6 weeks. Take them outside and hose them off, or if that's not possible, put them in the shower and shower them off with cool water. Then let them drain well and put them back where they were. It helps prevent spider mites as they're attracted to dusty plants. And your plants love the rinsing off!

Water them only when you are sure the soil is close being dry down to the bottom of the container. you can stick some kind of wooden stick into the soil and let it set for a while. If it comes up damp with soil stuck to it, then there is plenty of moisture in the soil. If it comes up mostly clean and you don't see much moisture on it, you know it is time to water. After a while, you will pretty much be able to just pick up the container and judge how wet the soil is by how light or heavy it feels. Just don't keep them soaking wet and don't let them completely dry out. If you keep a close watch, the plants will tell you when they are drying out but with seedlings it is more critical to watch them close. With full grown plants, they can take lack of moisture better. Tendency for new growers is that they tend to over water. Bruce