What Are Brownish Red Chevron Pattern On Several Leaves?

Question

Birds nest fern leaves up to 30”. Vigorous growth
continuing.

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Answer 1

That looks like a bacterial spot from overwatering. I would cut back just a little.

Since these are epiphytes and normally reside attached to trees, they can handle some drying out, just not for very long. You can cut any infected leaves once they spread over half of the leaf. Treat with a light spraying of fungicide. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm