My first impression was fungus growth, possibly Pythium Root Rot but the roots in the pic don't show any blackening that I can see. Are the plants themselves showing any problems? Wilting? Softening of the stems? Has it been exceptionally wet or is the soil there unusually slow to drain? Both can encourage P. root rot. But sometimes as the soil dries new roots will develop and the plants will recover. If that is the case then a good fungicide application will help the plants recover IF the soil can dry out. Dave

Be sure to dig it out and bet the entire bulb/colony underground, you'll have it all over if you don't. It can spread like wildfire and everytime you mow your lawn you'll smell onions!

Immature spittlebugs (also called "frog hoppers"). They feed on the plant's sap, although there aren't usually all that many of them in one place that they cause a lot of damage (as far as I can recall).

All of those methods may work but even if you kill them off you still have a nasty film on the leaves. Unless you have a palm so big and heavey you cant move it, it only makes sence to take it out for the summer. months of rain really clean it up. In addition you will get your strongest growth out of it. I have a double roebi that has about a foot of trunk and is ablut 2.5 feet overall. They were languishing in a grocery store parking lot when I got them last October for 8 bucks. I had to cut off quite a bit of the fronds as it was pot bound, under-watered, and getting no sun. I repotted it and it made a SLOW comeback over the winter. It's been outside in full sun since the first week of May and it looks good as new. it has already become one of my most attractive palms.