AI generator gave this when searched Mexican fan palm,dying spear. Might be more specifics in links.

"A dying spear leaf on a Mexican fan palm can be caused by a number of issues, including:
Phytophthora bud rot: A disease that starts as a leaf spot on the spear leaf, and can lead to the spear leaf dying or declining. This disease is more common in nurseries than in the landscape.
Extreme temperatures: Freezing winter weather can injure the spear, which is the youngest part of the tree.
Lethal bronzing: A destructive new palm disease that can affect the spear leaf.
Here are some other things to consider when caring for a Mexican fan palm:
Watering: The soil should be moist but not soggy. Inconsistent watering can lead to wilting and leaf issues.
Light: Mexican fan palms prefer bright, indirect light.
Fertilizing: Fertilizer can help the palm tolerate cold temperatures.
Pests: Regularly inspect the palm for pests and use natural or chemical remedies.
Fronds: Avoid removing fronds unless they are brown and dead. Palms need their old fronds to support new growth."