Hi I'm also on Kauai.
I just use safer's soap, and that usually gets rid of soft scale. I'm not big on using nasty chemicals, so I don't use them on my plants
If it's a potted palm, it may be small enough to spray rubbing alcohol on the fronds, which will eliminate most, unless they are really mature armored scale.
In that case, you might need to use something a little stronger.

I hope that helped.
Aloha, Christine

If the infestation is really bad. I would cut the fronds off and destroy them. If possible burn or bury to kill the scales on the affected leaves. I used Malathion but have heard of insecticidal soaps being used. in the local newspaper here, there was mention by the state Ag. dept that a certain type of ladybug was being propagated as a biological pest control to be used against the sago scale. I have seen a lot of mature sago palms, and queen sago palms die because the owners do nothing and just allow the scale to kill the plant. We never had this problem before. I had heard that it originated in Maui. But the ladybug solution seemed to have worked there. I am uninformed except for being a victim of the scale attack, and the things that have worked for me here in Hilo. This pest is a tenacious one and needs to be seriously attended to if you wish to keep the plant and the pests in check. Goodluck with the project.

Try a systemic insecticide such as Merit. It can be sprayed directly on the plant or as a drench. Be sure the plant has not been watered prior to use. It cannot reverse the damage, but Merit will stop it for several months. We use it on our native Hawaiian plants which can be sensitive to some insecticdes. Merit is pricey, but the small container of wetable powder goes along way and works!

We have the same thing here in Florida. I've been using Neem + Horticultural Grade oil + Pyrethrum concentrate with great results. You have to spray all the surfaces, especially the undersides of the leaves including the trunks. The following week, I use water to blast the scale and fuzz on the crowns off (careful spray on the leaves not hard blast or they'll be damaged.)
Have had 16 to last for the past 4 years stay alive when most of the ones in the state have died.
kevin

Hi from Kauai
We treated with Triple Action and it made no difference...wrong product :( We then cut all the fronds off and treated the trees with Tick and Fleaa control for yards. The Sagos looked pretty funny for awhile but the new fronds are FINE. Worked for us...may work for you :)
NANinHI