I have a wonderful ponytail palm tree that has been growing well for me for years. But it has developed a weird problem lately, and I am not sure why. I have noticed dead, brown spots on the fronds, mostly in horizontal stripes across the width of the frond. This is unusual in that most of the dead spots are up near the tops of the fronds. Usually I only get brown spots on the tips and lower fronds. By the time I catch them, the dead spots have usually spread across the entire frond and it is about to fall off. I’ve already lost a few fronds, and it is continuing to happen regularly. I don’t know why this is happening. I don’t see any bugs or signs of infection and the plant seems otherwise healthy. Any ideas?