Question
QUESTION: I have some leatherleaf ferns that have some clorotic and later necrotic, even watersoaked lesions on the foliage.    Symptoms include the necrosis and clorosis I mentioned, and also a failure of the leaflets to form and expand--they just rot. And it can hit fronds that are just a couple of inches tall to over a foot tall.  The only ones it doesn磘 seem to attack are fronds that have already matured (more rigid stem and dark green foliage).

I can磘 see a trend in the distribution in the planting (this is field production under a 50% shade cloth) either with respect to the topography of the site or other spatial factor.  The disease affects tissues of different ages, but always immature stems (never seen on mature stems).

I sent some samples to a lab and the results indicated Cercospora rot or Rhizoctonia spp., but neither of those feels right because Cercospora usually causes spots with yellow halos and rarely wet necrosis.  The Rhizoctonia sounds strange as it is usually a soil pathogen, and doesn磘 attack foliarly, but could cause that type of symptom.  However, I did find some literature (U. of Hawaii) that seems to indicate that Rhizoctonia can attack even upper foliage.  A different guess would bee Calonectria or Cylindrocladium, but I don磘 have much experience with those diseases.

I am going to try to take some photos to send to you for a better description of the symptoms.


ANSWER: Dear Jeff;

For obvious reasons, I cannot offer definitive disease diagnostic assessments from a written description.  Naturally, if you are able to send some photos, it would help.

However, everything that you have indicated (other than the lab results) leads me to believe that your field may be infected with Fern Anthracnose (Colletotrichum).  I have (unfortunately) seen it before and it is quite difficult to eliminate or control.  There are a few registered fungicides that may help, but they all provide partial control and have potential side effects.  Also, I am not familiar with the availability and regulations regarding pesticides in your locale.

Here are links to a couple of relevant articles; let me know what you think:

http://www.mrec.ifas.ufl.edu/cutfol/cutpubs/ppc372.htm

http://www.mrec.ifas.ufl.edu/jos/Section_3.htm

http://mrec.ifas.ufl.edu/jos/Bulletin%20900-PDF/SECT_5.pdf

I am not usually a fan of lab tests, because I have found that they oftentimes point to a secondary pathogen that has settled on blighted site, rather than the disease agent itself.

However, if your symptoms do not match those for Anthracnose, I would suspect Rhizoctonia as a second culprit (based on your test results).  In ferns, this disease does, in fact, manifest itself as a crown and stem mold (rather than being root-borne).  It is the most typical problem in basket production of Nephrolepis.  I have to mention, however, that I have never seen it on leatherleaf and that the symptoms you describe do not seem typical.  I would expect it as a rot starting from the inside and working its way out, rather than the tip damage you describe.  There are many registered fungicides for control of Rhizoctonia, and good irrigation management can usually get half the work done.  However, as mentioned, I think it is unlikely that this is your problem.

Some growers had similar problems on Japanese holly and tassel ferns, and have enjoyed minor, temporary success by using copper sprays.  Accordingly, they have concluded that the disease you describe is bacterial. I have found no empirical support to this theory, but I would try a small scale trial to see if you have some disease management and no leaf damage (keeping in mind that some copper formulations may be PHYTOTOXIC to ferns in certain conditions).  

While unlikely, there may also be physiological causes to your problem.  Some growers in Europe claim that the phenomenon you describe is heat-stress related and is a result of the young fronds inability to keep themselves hydrated in summer months.  Others mention calcium deficiencies.  While I give credence to the theory that these are contributing factors, I tend to believe there is a pathogen involved (possibly endemic at this juncture).

Please let me know if any of my theories feels correct, and if you need more information regarding control measures.  Alternatively, if you are able to outrule these possibilities, I may be able to search for other alternatives.

Thanks for your challenge, and I hope things work out!

DC

---------- FOLLOW-UP ----------

QUESTION: Hi Dan,

I actually continued digging and arrived also at Fern anthracnose.  This is the right pathogen, and the symptoms from the pictures I could find are right--the lab got it wrong.  And you are right--this disease is going to be difficult to manage.  It is going to require some serious integrated management.

In my searches, I also ended up at the MREC, which makes sense because they have so many ferns in Volusia County.  I had looked a bit trying to get there before, but never had quite the right key words.

Thanks for your confirmation.
Jeff

Answer
I am sorry to hear this confirmation...but at least you are on the right track.

The fungicide Heritage (Azoxystrobin) is specifically labelled for both the pathogen and crop you deal with.  The downsides are that it is CRAZY expensive and does have unintended consequences (leaf greening and deformation)...I cannot even say if it is cost-effective in field applications.

I think the MREC links provide the fullest control methodology but please feel free to follow up if you require further advice or assistance.

DC