I have several large Kentia Palms, ranging from 6' to 15' of trunk growing in my yard. They are getting a hard brown scale that starts near the bottom and moves up the trunk. It looks more like brown paint specks than the scale I have seen on houseplants. Where the scale has died off, the trunk is gray. The scale does not affect any other plants, even the Bromeliads growing on the trunks.
Hard Brown Scale on Large Kentia Palm
Certified GKH Gardening Expert
Try pruning out any discolored leaves. Neem oil is also effective treatment for the scale issue. This article will help you with the scale: https://www.gardeningknowhow.com/houseplants/palms/sticky-palm-tree-leaves-treatment-for-palm-scale.htm