From: "Peter Matthews" pjm at gol.com> on 2006.07.09 at 04:15:43(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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On 8/7/2006, "Adam Black" wrote:
>
>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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