Ferns: Sword fern - brownish leaves

Discussion in 'Plants with Spores (Ferns, Mosses, et al.)' started by Margot, Nov 14, 2019.

  1. Margot

    Margot Generous Contributor

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    Again this year, I see some of my sword ferns (Polystichum munitum) are becoming brownish. It doesn't look fungal to me nor are there any signs of spider mites so I'm wondering not only what the cause may be but also whether it might spread to the unaffected sword ferns nearby. All the better if it is preventable or curable. The ferns get regular watering through the dry months and have excellent drainage. They are growing in bright semi-shade.
    Except for being unattractive, the plant seems perfectly healthy.
     

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  2. Sulev

    Sulev Active Member

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    Maybe they got more direct sunlight than expected after the "bright semi-shade" crown cover (oaks?) above dropped its leaves, in combination with too few precipitation?
    According to the Weather in October 2019 in Vancouver, British Columbia, Canada there was ca 20 days long period without any rain in the Vancouver area.
    Maybe your ferns don't just like this kind of exposure to the sun together with cold soil (obtaining water from the cold ground is difficult) and autumn winds? October, 25th was possibly the hardest for ferns, relatively strong winds together with sunshine and relatively cold soil.
    Last picture is of the sporangia, these are no signs of illness.
     
  3. Ron B

    Ron B Paragon of Plants 10 Years

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  4. Margot

    Margot Generous Contributor

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    Sulev - I really appreciate your thoughts but the fact is that many of my sword ferns growing in almost full sun are still perfectly green. I think you're right that it could be a combination of challenges . . . the ferns on the bank where the browning one is located are quite old and I wonder if there are enough nutrients in the rocky soil where they self-seeded (self-spored?). Otherwise, the growing conditions in my garden are very benign; zone 8b-9a.

    Ron - the mystery problem you mention is very worrying and I sure hope a cause is found soon. I'll watch for fronds wilting and/or fiddle heads dying but right now it looks very healthy (except for the browning).

    For now, I'll keep an eye on my fern and try to figure out what else might be at play. At least I can now rule out the likelihood of pests or diseases.
     
    Last edited: Nov 14, 2019
  5. wcutler

    wcutler Esteemed Contributor Forums Moderator VCBF Cherry Scout 10 Years

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    Your question implies that they don't go brown every year. I'm so surprised to read that. I thought they all lost lots of fronds in the winter and got lots of new fronds in the spring. Not so?
     
  6. Margot

    Margot Generous Contributor

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    Polystichum munitum is an evergreen fern. The browning that I see now, especially on the edges of pinnae, is quite different than leaf senescence. Depending on how harsh the winter, sword fern fronds can stay green for a couple of years although they tend to look increasingly tattered as time goes by.

    I try to remove the old fronds just before the new ones are ready to emerge but I'm sure ferns would prefer the old leaves be left as mulch. Fern fronds make a fabulous mulch/compost.
     
  7. Ron B

    Ron B Paragon of Plants 10 Years

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    Partial browning of existing fronds during the winter and spring removal of these by persons concerned about how it looks is typical for cultivated specimens of this plant here in its native area.
     
  8. Sulev

    Sulev Active Member

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    Those of your ferns, who spent whole summer in the sunshine, did not get sudden change in light exposure and moisture conditions in the autumn, after deciduous trees dropped their leaves. Plants often have different leaf structure (number of stomata per area etc) if growing in the shade, compared when growing in the direct sunlight. This can have effect on what is their resistance to drought conditions, even if it is not exactly a meteorological drought but physiological drought.
    physiological drought - Dictionary of botany
     
  9. Ron B

    Ron B Paragon of Plants 10 Years

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    Friend's property on Camano Island - where they seem to share in weather patterns occurring in the Lower Mainland at least part of the time - has other kinds of plants that got discolored by some circumstance this year also. As with your ferns looking as though already affected by significant winter cold, even though it has been for the most part unseasonably mild.
     
  10. barrolini

    barrolini Active Member

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    I came across your posting of last year. I have many, many ferns in my hillside yard, and am in the midst of having the fronds on too many of them turning from brown to virtually black. The brownish "stage" ones look identical to yours. I am wondering what happened to your ferns since last year. I am reluctant to dig them all up, and your experience since last year may would be much appreciated.
     
  11. Margot

    Margot Generous Contributor

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    Would you be able to post 2 or 3 photos of the blackening fronds on your ferns? Are you positive that they are Sword Ferns (Polystichum munitum)? I can understand why you'd be worried, especially in light of what @Ron B posted in #3 above: Sword Fern (Polystichum munitum)-Die-off

    I've come to the conclusion that the browning on my Sword Ferns that begins to occur at this time of year is normal for them. Eventually the fronds on all of them begin to brown. I've uploaded a few current photos. The fact is that these ferns get plenty of water year round and are growing fast so I think they are healthy.

    I hope you will soon be able to say the same about yours.
     

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  12. barrolini

    barrolini Active Member

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    Thank you for your response, Margot.. I have many ferns, the vast majority are sword fears. My subsequent research, and the severity of the problem on many, suggests to me that I may have a nematode infestation, either in the foliage or the roots. I have since dug up about 15 affected ferns from the area of the large yard, and will be monitoring the others closely. I am showing the good and the bad, and apologize for the clumsiness of the image posting; first time for everything! IMG_1726.JPG IMG_1724.JPG
     
  13. Margot

    Margot Generous Contributor

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    Very interesting - never heard of such a possibility so I'll try to find out more and see if that could be an issue with my ferns. Thanks for the information.
     
  14. scilover

    scilover Member

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    Very interesting and beautiful. even though they don't have flowers, they do look spectacularly beautiful.
     
  15. Georgia Strait

    Georgia Strait Rising Contributor

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  16. Patrick McDonnell

    Patrick McDonnell New Member

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    I am in the coastal hills above San Francisco. We have north facing, wooded hills that have long been covered in sword ferns, likely 10 acre contiguous zones on our property alone. This is the first year in which many acres of the ferns have had a majority, to all, of their fronds turn brown and dry. The whole plant looks dead. We are seeing the first rising of new fiddleheads now, but some seem not to be thriving. We are seeing this on other nearby properties, but not as extensive.
     
  17. Acerholic

    Acerholic Esteemed Contributor Forums Moderator VCBF Cherry Scout Maple Society

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    @Patrick McDonnell good morning Patrick and welcome to the forum. If you could post some photos of the Sword ferns, that would be very helpful for members to perhaps identify the problem. If you are unsure how to do this I have added a very good tutorial link to help you through this process.
    Attach photos and files
    In the meantime the postings by @Georgia Strait are a very interesting read and might point you in the right direction.
    The Case of the Vanishing Ferns: Citizen sleuths can’t figure out what’s killing Seattle’s sword ferns

    Seward Park Sword Fern Die-off
     
  18. Georgia Strait

    Georgia Strait Rising Contributor

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    Good morning - I imagine you mean the coastal hills of Marin ? I really like the wooded areas along (currently named) Sir Francis Drake Blvd (Samuel P Taylor state park)

    One thing I wonder - before thinking it’s THE sword fern disease - is did recent longterm Calif drought make a difference to your area ? I wonder if other forest plants on your swath are looking stressed too.

    Has anyone logged or changed land near you recently (which can change drainage)

    Our sword ferns - once established in garden - seem fine today and rarely need water in our dry summers nr Vanc BC (plus we have lots of winter water out of the sky)

    Tho I did kill a couple new nursery transplants last summer due to careless lack of water

    I found this article (below) interesting fr your area — tho I have never seen a 5-foot tall sword fern as cited in article. Amazing!

    Ours are commonly 3x3 feet here. Yes, some brown fronds to trim off each spring but generally the ones in garden here nr ocean Vancouver BC are looking healthy green vigorous

    Native ferns bring woodsy vibe into gardens – Marin Independent Journal
     

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  19. Margot

    Margot Generous Contributor

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    The problem with fern leaves turning prematurely brown in my garden is getting worse - not THE sword fern disease that is killing ferns in areas south of the border but worrisome all the same. I don't see the same thing going on with wild-growing ferns in the area. I've grown dozens of Polystichum munitum over the years and this is something I've never seen before. Ferns growing in full sun are affected and also some in lots of shade. They get plenty of water - perhaps too much. The browning starts to get a lot worse in late summer but the ferns themselves are otherwise healthy.

    Perhaps it is nematodes as @barrolini suggests in post #12 but I wouldn't know how to check that or what to do about it if it is. I'm going to cut all the old fronds off soon and take them to the yard waste facility.
     

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  20. Patrick McDonnell

    Patrick McDonnell New Member

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    Here are three pictures illustrating the apparent disease progression in our coastal California hillsides. The photo titled "Detail of disease progression in fern fronds", it is possible to see the non-uniform browning of the fronds, both within each affected frond and between fronds. In the photo title "Early stage Bowning of fronds", it is possible to see how the disease progresses in a close-up of a group of ferns on the periphery of the area of primary impact. In the photo titled "Disease progression lower to higher on the hill", one can discern that from this peripheral area of the primary diseased zone, one can look up the hill and see ever more severe browning of the fronds. I believe that all of this is presenting itself in a single season

    The question is whether this may be a temporary setback to the ferns or whether something more long term has hit and our sun-sheltered hillsides near the coast may be entering an entirely new ecological phase with the elimination of vast expanses of ferns.

    Other contemporaneous changes to the forest that have been occurring over the past couple of years include the complete decimation of tan oak and the near elimination of coastal live oak due to Phutophthroa ramorum, their replacement in most zones by new Douglas fir and the explosion of poison oak through-out the forest. These changes have been sudden, but on a time frame of several years, while the changes to the ferns seems to be nearly instantaneous.
     

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  21. Georgia Strait

    Georgia Strait Rising Contributor

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    @Patrick McDonnell

    Gosh those photos are shocking

    How discouraging

    I have not read up enuf to find out when & where the scientists think this may have come from and how it spreads
     
  22. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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  23. Sulev

    Sulev Active Member

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    Looks like a frost bite.
     
  24. Patrick McDonnell

    Patrick McDonnell New Member

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    a follow-up on the prior posting about fern die-back in central coastal hills of California.

    Regarding suggestion of frost as a culprit, we are in an area in which frost is a 25 - 40 day per year event in exposed areas of our valley floor. It almost never gets down to 20 degree F in the exposed valleys. In fact, on these tree covered hillsides, well above valley floors, frost is extremely rare. 15 years ago, frost was more common and temperatures below 20 degrees F were infrequent, but not uncommon. The ferns in their primary north facing hillsides thrived in that environment. In the last several years, their areal extent has been expanding with many small ferns showing up in non-north facing zones.

    At Daniel Mosquin's suggestion, I reached out to Pittermann Lab at UCSC. Dr. Pitterman suggested the pattern of dieback was not consistent with drought, but thrips were a potential cause. I believe on closer look, that her guess correct (see phot0). There are areas of this frond that had many clustered together. Based on a USDA ID guide, these look like the greenhouse thrip, which includes Southern California in its native range. I am wondering,if the ID is correct, whether the warming winters may be allowing them to move north. Dr. Pittermann suggested that the thrips, if the culprit, may burn themselves out, based on the extensive damage they have been doing, and the root reserves of the ferns may permit them to make a comeback.

    It will be interesting to see how this infestation expands beyond our property to other areas, both how fast and how extensive.
     

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  25. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Thank you for the follow-up! I'm glad the Pittermann lab was able to help.
     

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