Overview

A mixed lay/scientific group here in Seattle (Seattle Parks ecologists, UW researchers, the Friends of Seward Park) is trying to figure out an unprecedented and alarming sword fern die-off in one hundred acres of old-growth forest in Seward Park.  The affected area is spreading radially; lush understory of two years ago is now bare ground.  Drought, pollution and mountain beaver activity may be contributing factors, but deeper and as yet unknown causes appear to be at play.

Survey: October  2014

Fronds in Detail: October 2015

This blog serves to document and  present our work.  Please contact paul.thurmond.shannon@gmail.com for further information.

Candidate Sword Fern Pests 

Provided by Jenny Glass, from the USDA-APHIS Fungal-Host Database

I am not sure that I ever sent you the list of possibilities that I went through during your DEC 2014 submission:

The literature generally suggests the species Polystichum munitum is relatively disease and pest free and an investigation of other Polystichum species revealed more or less the same information.  As discussed, the laboratory investigated a similar concern about dying sword fern in the Jefferson County area in 2013.  We were also unable to pinpoint the origin of that damage beyond the impression that the sample contained no apparent disease or pest origins of damage.  

The USDA-APHIS Fungal-Host Database had these fungi listed as being observed on sword fern but none of the described fungi are likely to be associated as the cause of this patch of dying plants.

Chaetasbolisia falcata:  Polystichum munitum: California 

Helotium polystichi:  (Basidiomycete):

     Polystichum munitum (On stems.): California 

Herpobasidium abnorme:  (reported to cause distortion):

     Polystichum munitum: Idaho - 

Milesia polystichi - (Milesina winelandi):   (rust- obligate parasite unlikely to kill host)

     Polystichum munitum: California, Canada, Idaho, Montana, Oregon, Washington 

Milesia vogesiaca - (Milesina vogesiaca): (rust- obligate parasite unlikely to kill host)

    Polystichum munitum Canada, Oregon  

Milesina vogesiaca:  (rust- obligate parasite unlikely to kill host): 

    Polystichum munitum California

Milesina winelandi:  (rust- obligate parasite unlikely to kill host):

    Polystichum munitum: California, Idaho, Montana, Oregon, Washington  

Mycena fragillima:  (small saprophytic mushrooms): 

    Polystichum munitum: California, Oregon, Washington  

Phoma adianticola - (Didymella adianticola):  Phomopsis sp.: 

    Polystichum munitum (On fronds.): Oregon 

Phyllosticta sp.: Polystichum munitum (On fronds.): Oregon 

Phytophthora cinnamomi:  (thrives in saturated soils/poor drainage):

     Polystichum munitum (Root rot.): California 

Pythium sp.:  (thrives in saturated soils/poor drainage):

    Polystichum munitum California  

Rhizoctonia solani: (frond blight is a common symptom): 

    Polystichum sp.: California 

Taphrina faulliana: (leaf blister): 

    Polystichum munitum: Canada, Idaho, Oregon, Washington  

Valdensia heterodoxa: (apparent leaf spot/leaf blight pathogen):

    Polystichum munitum: Canada 

Xenasma filicinum - (Phlebiella filicina): 

     Polystichum munitum: Canada

Lab Report from Jenny Glass (12/04/15)

Dr. Marianne Elliott's Report (12/3/2015)

I have attached the sampling procedure and list of samples we collected. We did not find any Phytophthora, but I am not ready to rule it out as the cause of the die-off. It could be a species that is slow growing and difficult to culture, so we missed it. Or it was replaced by something else in dead material. Or this was the wrong time of the year to sample. I think the students who are working on this should keep an eye out for it.

There were a few Pythiums and other similar organisms that we see commonly in soil and roots. We didn't find anything associated with the dying sites vs the healthy sites, or with the dead cedar transplants. I have been asking various people I know and nobody has seen it in their travels, but now they are aware of the situation. I will let you know if anything turns up.

--Marianne

Sample Processing Protocol (Sword fern dieoff samples collected at Seward Park 11/10/15)

Sample #	Description	Treatment
1	5 x 5 plot, healthy, symptomatic fern foliage	Surface sterilize, plate 5 segments on PARPHV8 (3 plates)
2	5 x 5 plot, healthy, crown from healthy fern plant	Surface sterilize 10 necrotic root segments per plate (PARPHV8), dissect crown and look for brown staining symptoms (3 plates). If present, surface sterilize and plate 5 segments on PARPHV8 (1 plate).
3	5 x 5 plot, healthy, soil from base of 3 healthy ferns, upper 5 cm depth + litter & roots	Bait in 1 L bottles. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water.
4	Ground zero, foliage and fronds from dying ferns	Surface sterilize, plate 5 segments on PARPHV8 (3 plates)
5	Ground zero, crown and roots from dead ferns	Surface sterilize 10 necrotic root segments per plate (PARPHV8), dissect crown and look for brown staining symptoms (3 plates). If present, surface sterilize and plate 5 segments on PARPHV8 (1 plate).
6	Ground zero, soil from base of 3 dead ferns, upper 5 cm depth + litter & roots	Bait in 1 L bottles. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water.
7	Ground zero, soil from base of 3 dead, planted cedars	Bait in 1 L bottles. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water.
8	Symptomatic foliage from other hosts along trail by Ground zero and road	Surface sterilize, plate 5 segments on PARPHV8 (3 plates).

Baiting protocol for soils

Label 1L bottles with sample and rep numbers. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water. Cap tightly and incubate bottles on their sides for 48-72h.

After incubation, remove baits from bottles and rinse with water, then blot dry. If asymptomatic incubate an additional 3-7 days in ziplock bags containing moist paper towels. Plate symptomatic areas of foliage (5 per plate) on PARPHV8. Use two plates for each bait type per bottle.

All samples

Check for Phytophthora colonies on all plates after 2-5 days and isolate onto small PARP plates for identification.

A mixed lay/scientific group here in Seattle (Seattle Parks ecologists, UW researchers, the Friends of Seward Park) is trying to figure out an unprecedented and alarming sword fern die-off in one hundred acres of old-growth forest in Seward Park.  The affected area is spreading radially; lush understory of two years ago is now bare ground.  Drought, pollution and mountain beaver activity may be contributing factors, but deeper and as yet unknown causes appear to be at play.

Survey: October  2014

Fronds in Detail: October 2015

This blog serves to document and  present our work.  Please contact pshannon@systemsbiology.org for further information.

Site Visit by WSU Plant Pathologists Marianne Elliott and Jenny Glass

Tuesday November 10th, Dr. Marianne Elliott and Jenny Glass (Diagnostic Plant Pathologist) braved the traffic and drove up to Seward Park from the WSU Plant and Insect Diagnostic Laboratory in Puyallup.

Accompanied by undergraduate students Tristan O'Mara, Kramer Canup and me, Marianne and Jenny spent a couple of hours inspecting the extended die-off site, and collecting soil and leaf samples from affected sites and a mostly healthy region (Kramer and Tristan's 5x5m "Plot 1").

Jenny describes her self as a lab generalist (a most expert generalist, it seems to me).   Marianne is a research plant pathologist who, among other things, has coordinated (and is celebrated for) Washington's statewide response to Sudden Oak Death.  She is active in phytophthora research.  Though previous tests for Phytophthora came up negative (Jenny in 2014, Olaf Ribeiro in spring 2015) Marianne suggests that a closer and more sustained examination is worthwhile.

The site visit resulted in what is, at present, a very tentatively held hypothesis.  Marianne noticed small and mostly dead cedar seedlings, about 12 inches tall, each marked with a red-on-white plastic tag, in and around ground zero.   We found several of these up above the north-facing ground zero slope, the flat area where Catherine Alexander first noticed signs of distress and die-off.

Lisa Cieko learned from fellow Parks plant ecologist, Michael Yadrick, that these tagged cedar seedings were among 10,520 bareroot cedars Parks contractors had planted throughout the forest in February of 2011.  Lisa adds: one article that I found did says that this could be an issue -

      Root Rot of Western Swordfern Caused by Phytophthora cinnamomi in California.

The abstract mentions that the "pathogen was inadvertently brought to the site via rhododendron nursery stock".    

Thus we have a conjecture, a  hypothesis,  and the good fortune to also have experts both skilled and experienced to test it out.   Their lab methods may also reveal other candidates, may suggest other hypotheses.   We are very grateful to Marianne and Jenny!

A very helpful email exchange with Dr. Rodrigo Valverde of the LSU Department of Plant Pathology and Crop Physiology, November 8th, 2015.   Rodrigo published a discovery of a novel fern virus in 2008:  New Virus Causing Disease in Japanese Holly Fern.

 Questions from me are in italics, and Rodrigo's answers are in bold.

Finally I have some time to answer your questions. I talked to other plant pathologists and in general they agree with my thoughts about the fern problem. Ok, below are your questions and my answers.

The ferns appear to die over about 12-24 months — that is, they go from good health to full death in that length of time. Is this faster than what you saw in your 2009 paper?

The time is similar but the fern virus does not kill the ferns (entirely) only several leaves followed by a slow decline which may end up in death.

We do not see any insects around the plants, but I will look again knowing now that the usual suspects do not seem to be present.  Have you any tips (or suggestions of things I can read) in order to do a good job on insects?

Unless they are vectoring a pathogen, it is unlikely that insects will kill the ferns. And if that is the case, they (the insects) will be very visible.

Our local plant pathologists are stumped.  Are there standard strategies for tracking down as yet unrecognized fungal, bacterial or nematode causes?  

Yes and no! Most new pathogens are old on pathogenic agents that evolved into a pathogen due to changes in the environment. It is very difficult sometime to differentiate between a pathogen and a saprophyte.

Maybe things like:

  1) look at a completely dead fern for lingering pests,  or
  2) look at an only partly affected fern (under the assumption the pest is still operating, and can be more easily found)
  3) culture in the lab for fungus & bacteria, hoping they will grow until they can be recognized.

These points (2 and 3) make a lot of sense and I am sure that the plant pathologists there are considering them. However, if an abiotic factor is involved as primary cause, they will not work. 

or anything else, any other strategies?

My impression is that it could be a soil-borne pathogen or a soil abiotic factor (pH, salinity, etc) or a combination of both. The abiotic factor allows the "new" pathogen to thrive!  Soil nutrient analysis including pH will may provide some information.

Good luck and keep me posted of any new development of the fern problem.

Rodrigo