Sword Fern pest?

Question: I have been seeing the tips of several, but not all, of many sword fern fronds either broken (so they are hanging) or stripped of foliage. The remaining frond sections are vibrant and healthy in appearance. It seems like an insect of some sort, but in searching I find no references. However, this post from 2014 shows exactly what I am seeing. That post is unresolved. I'm certain it is not deer - we have a fenced yard that is inaccessible to them. https://ask2.extension.org/kb/faq.php?id=208790. Do you have any information that has come to light in the past 9 years, or is this still something of a mystery?

I've attached two photos. The sword fern pictured has a couple of broken tips visible along with some stripping of another frond. There is a lady fern nearby with a couple of fronds with dead tips. I can't know it is the same cause, but thought it might be interesting to include. The vast majority of our ferns are fine, so it's difficult not to suspect a bug or larva. Sawfly? Given it's not widespread (at least not yet), it's not a huge concern but solving the 2014 mystery would be nice.

Thanks.

responder: Jacki D., Master Gardener Diagnostician Volunteer (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (http://metromastergardeners.org/) Replied June 07, 2023, 9:49 PM EDT
response: I don’t have the mystery of fern damage solved (yet). The tip dieback happens on some of my fern, but never enough I’ve really questioned it. More detective work may resolve things. Can you tell how early the tips died? Maybe the stem was damaged in fiddle head, then the balance of the frond rolled out successfully. Go out after dark a few times with a flashlight to look for insects, cut worms, snails, slugs. I see a deformed frond, and what looks like clipped bits. Could it be rodent snacking? “Predators Deer and rabbits will eat sword ferns, along with other rodents. The Washington Dept. of Wildlife has a handy table that provides a list of plants that are eaten by Mule, and Black- and White-tailed deer.” See this OSU blog, which is the source of the quote. How to confirm animal damage? A trail camera? Sorry, I don’t know how to fix the print size in this forum. Hope to hear back from you with any discoveries. I tried to mark up your photo to show the parts I noticed. Maybe it helps?

responder: The Question Asker Replied June 08, 2023, 1:35 PM EDT
response: Hello Jacki, Thanks for the info. I will try some nocturnal discovery, but the damage must be at least a few weeks old by now, possibly a month or even more. We trimmed the old fronds end of March into April depending on how fast the new fiddles were appearing. I don't recall seeing any damage to them as we worked, but I might have missed something. In the photo you marked up, there are two more fronds broken near the tips at the bottom of the photo. One is still dangling from the rest of the healthy frond behind it. You've correctly marked the areas where the fronds are stripped of foliage. Are both forms of damage from the same cause, or are two culprits at work? It was the dangling tips that caught my eye.Rodents isn't impossible. We've been here 23 years now, and have only seen a rabbit once many years ago. But there are some rats about plus any native voles, mice, etc. Our fences are too tall for deer. And why bite the tip only to leave it on the frond? Odd... The only factor I come back to around an insect being the cause is that the ferns affected by this are in a rather localized area of the backyard. We have a large, pie-shaped back yard on a cul-de-sac (Backyard Habitat Platinum Certified, woohoo) and we have dozens of sword ferns throughout the yard. The affected ferns are in a 10' x 25' bed at the side of the house. Slightly more light exposure than most of the rest of the yard, but still shaded. Same soil, water, etc. I walked around yesterday again, and not a single other fern frond is affected away from this area.So, I'll place a bet on some insect that occasionally causes this - whether after unfurling or, as you posit, while the fiddle heads are still folded. But, again, why bite the stem and leave the tip dangling?Thanks again for the info. It's not a widespread issue, not really important even for now, but my curiosity remains. Sword ferns seems so bulletproof that something like this jumps out a bit.On Wed, Jun 7, 2023 at 6:49 PM Ask Extension <<personal data hidden>> wrote:

responder: Jacki D., Master Gardener Diagnostician Volunteer (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (http://metromastergardeners.org/) Replied June 09, 2023, 12:54 AM EDT
response: Keep me posted about what you find. I have a resident wild rabbit but don’t see fern damage … yet. I did see a couple of fronds in my front garden that were brown and dangling, but only tiny tips, and in a sunny spot where I’m expecting it’s heat or drought damage. My experience is anecdotal, when as Master Gardener I need to offer scientific information. This is an issue I’m not finding much about.