sago palms browning
I have many large Sago palms that have been growing in the ground for many years. Recently, just after a new set of fronds came out, two of the plants started getting brown sections on the fronds. There is no pattern to the brownness. A frond might have every other leaflet brown or just the tip or the middle and then dark green. The older lower fronds were not affected. There does not seem to be any scale, mites, fungus, etc. on them. It's very weird that only two of ten plants show this. Plants are at least 15 years old. Hope you can help.
Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/trees/sago-palm/how-to-care-for-sago-palms.htm