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Re: [Aroid-l] - Serious spreading Amorph disease-Collar rot

  • Subject: Re: [Aroid-l] - Serious spreading Amorph disease-Collar rot
  • From: Adam Black epiphyte1@earthlink.net
  • Date: Mon, 17 Jul 2006 02:23:15 -0400

Hi everybody,

I am a little late in thanking eveyone for their input on our diseased Amorphophallus. Seemed like the consensus was either an Erwinia bacterial infection or Sclerotium (Collar Rot) fungal infection, the latter suggested by Dr. Misra and detailed in his excellent article in Aroideana vol 26. The symptoms on our plants seem to match the Sclerotium more closely.

To those of you that requested photos of the infected plants,  I had planned to do so, but after my original posting to the list on this subject, I went back to work and could not find a single plant infected, and still have yet to see any more diseased plants. I am hopeful it has run its course. The symptoms appeared as we began receiving more regular rains after being in drought conditions for months here in north Florida, which correspond to Dr. Misra's description of changing environmental factors causing these outbreaks.

Though we weren't keeping track of numbers of casualties, our A. konjacs were hit the hardest, followed by A. bulbifer, but none of our A. paeoniifolius showed any symptoms. I had mentioned that most of our A. paeoniifolius were showing early signs of the disease, but upon closer examination, I figured out that the lawn service that maintains the grassy areas of the gardens had gone through with a weed-eater and trimmed the grass growing at the base of the petioles, whipping gashes in the base of the petioles. These injuries don't seem to be getting infected, and hopefully since the supposed Sclerotium outbreak has settled down, we won't see any more, for now at least. I still plan do do a soil drench with a systemic fungicide as Dr. Misra recommended just in case. And I have explained to the lawn service to keep their weed eaters away from the "giant celery lookin' things" as they called them.

Thanks again for everyone's help in this matter.


rajshekhar misra wrote:
Dear Adams,
The symptoms described by you are typical symptoms of
Collar rot disease of Amorphophallus caused by
Sclerotium rolfsii. We frequently observe this disease
in India. The Fungus is seed borne and also soil
borne. You might have seen white fungal mycelial
growth and mustard like structures called Sclerotia on
the infected surface. You can use systemic fungicides
like Carbendazim (0.1%) as soil drench to prevent the
For details, kindly go through my article in Aroideana
vol.26 on Field and Storage diseases of

--- Peter Matthews <pjm@gol.com> wrote:

Dear Adam,

Did your garden recenty import Amorphophallus
specimens from SE Asia or
other places where the genus is native? If you could
identify possible
geographical sources, this might help narrow down
the search for a cause.

Also, I wonder if there are any insects that lay
their eggs in the lower
petiole area? In theory, a newly spreading insect
might spread a new or
existing fungus. I do not know of such happening in
Araceae, but it is
conceivable. Taro has taro-specific planthoppers
(Delphacidae) that lay
eggs in the lower petiole, and they are spread with
planting materials
when the petioles are kept attached to the corm.
There might be
planthoppers that are specific to Amorphophallus
(this is speculation).

If  you want, I could try to contacting konyakku
researchers here in
Japan. There would certainly be interested in the
outbreak you describe,
even if it is something new for them. Or they might
recognise what is happening to your plants. There is
a lot of experience
with intensive production of Amorphophallus here in

Good luck...

Peter Matthews

On 8/7/2006, "Adam Black" <epiphyte1@earthlink.net>

We are suddenly having a severe problem with the
Amorphophallus species
at the botanical gardens where I work. We are
seeing a localized rotting
of the base of the petiole an inch or two above the
soil line that turns
the petiole base to jelly and topples the leaf. It
is affecting all
three species we have - A. konjac, A. bulbifer, and
A. paeoniifolius,
and is occurring in various areas of the gardens
that are seperated by a
considerable distance and have been otherwise
healthy in thier locations
in the ground for years. I started noticing it in
the konjacs and the
bulbifers a month or so ago shortly after they put
up thier leaves, and
the rate of loss has escalated from there. I just
now noticed on the
late emerging paeoniifolius that most of them have
early signs of this
infection. I am by no means an expert on fungi, but
there are several
different colors of fungus on the affected areas,
but I am not sure if
this is secondary or not. The infection starts out
as a brown patch on
the base of the petiole a few inches above the
soil/leaf litter line,
and this progresses around the petiole and inward,
but does not spread
up or down the petiole from that point. I dug up
one corm from an
infected A. bulbifer and it appeared shrunken in
and clearly unhealthy,
felt softer than a healthy corm but no external
evidence of rot was
evident. I did not cut it open to see what it
looked like inside, but
plan to on another specimen this week.The base of
the petiole below
where the leaf had rotted off was still healthy in
appearance and firmly
connected to the corm.

Curiously, I have yet to see it affect any similar
aroids growing
side-by-side with affected Amorphs in the gardens
including Typhonium
venosum (of which we have many plants), Gonatopus
bovinii, Remusatia
vivipera, and our native Arisaema triphyllum and
jillions of Arisaema
dracontium. The Amorphs affected include both
potted specimens and those
situated in the ground for years, and among the
potted specimens some
affected plants are in a greenhouse with controlled
watering, while
other potted plants are exposed to the weather in
addition to
supplemental irrigation. I am keeping a closer eye
on it now, but the
infection appears to spread and rot through the
petiole relatively
quickly, so that the leaf itself still looks
unstressed and perfectly
healthy after it has rotted off. I have only worked
here since this past
winter, but the gardens director remembers a few
Amorphs having this
problem last year but didn't think much of it, as
the hundreds of others
in our mass plantings looked fine. If I had to
guess now, I would say we
have lost about 60 or so plants with about as many
showing the early
stages of the infection. It also seems to affect
our mid to largest size
specimens rather than the smaller plants.

Has anybody seen this before? Any recommendations?
I am going to try a
fungicide this week, but with the huge number of
plants we have spread
out all over our 60+ acre gardens, I am worried
about how effective any
methods will be in controlling this. If anyone is
interested I can email
photos of affected plants in various stages of


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Dr.Raj Shekhar Misra
Principal Scientist & Head 
Crop Protection Division
Central Tuber Crops Research Institute
Sreekariyam, Trivandrum-695017(India)
Mobile Phone No. 91-9446557657
Phone-0471-2598551 to 2598554

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