[Aroid-l] Help - Serious spreading Amorph disease


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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