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  Help - Serious spreading Amorph disease
From: Adam Black epiphyte1 at earthlink.net> on 2006.07.08 at 11:05:21(14395)
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 infection.

Thanks

Adam

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From: "Peter Matthews" pjm at gol.com> on 2006.07.08 at 21:15:43(14396)
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 immediately
recognise what is happening to your plants. There is a lot of experience
with intensive production of Amorphophallus here in Japan.

Good luck...

Peter Matthews

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From: Tony Avent tony at plantdelights.com> on 2006.07.09 at 07:53:28(14397)
Adam:

I'd venture a guess that your culprit is a bacterial soft rot, Erwinia.
If so, fungicides are useless. I have seen this devastate collections
of certain amorphophallus species under certain conditions. It seems to
be worse when there is little air movement, lots of moisture, and high
humidity. I have even heard theories that it can be spread by the hands
of those who have handled tobacco or tobacco products. You will find
many references by using a Google search.

Tony Avent

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From: Susan B honeybunny442 at yahoo.com> on 2006.07.09 at 19:12:43(14399)
Hi Adam,
I lost my entire crop of konjacs to this about 5 years
ago. It affected the konjacs while other Amorphs
right next to them had no problems!
I've also lost a significant amount of Zantedeschia to
soft rot/Erwinia 2 years ago. The plants looked just
fine, until suddenly they toppled over at the base.
The petioles looked like they melted. I've also seen
it affect cut flowers- the plant looked fine, the
flower was picked and put into water in a vase. The
next day the petiole would have literally dissolved
all the way up to the spathe, which would look OK for
a little while and then it too would start to "melt".

My soft rot/Erwinia, which, by the way, I understand
is two different diseases but work together; seemed
different from your plant's symptoms.
First, the rot would progress up the petiole or down
to the tuber. I could pull the bloom and leaves right
out of the ground with no effort. Second, it has a
very awful, rotten, stinky smell. The tubers would
also be affected, with large sections rotting off.

Erwinia is a bacterial disease (if I remember
correctly), it is very contagious and can be carried
on feet from one site to another. Phyton 20, a copper
based formula, is said to prevent it, but bulbs must
be sprayed before planting. I believe if it affects
an area you are not supposed to use that soil again
because it is infected.

I did rescue a few of my tubers that weren't too badly
affected, I used a water hose to vigorously spray them
until all the mush washed away. Then I dried the
tubers in the sun/ air as much as possible. Some of
them were viable the next year, I only had about 3
plants with it last year as opposed to maybe a hundred
the year before.

Truly a heartbreaking disease. I wish you luck with
it. Since your tubers seem to be OK, you may have
some other disease or pest going on....

Susan B

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