The MGS Forum
Gardening in mediterranean climates => Pests and diseases => Topic started by: Nigel on May 30, 2012, 06:35:17 AM
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Can anyone help out to identify and suggest a treatment for the fungus that is damaging these oleanders?
Thanks,
Nigel
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Are you sure it is a fungus? It could also possibly be Oleander leaf scorch, which is is caused by the oleander strain of Xylella fastidiosa? I don't know where your oleanders are growing and if if this disease occurs outside the US, though. There is some information at http://ag.arizona.edu/plp/plpext/diseases/trees/oleander/oleleaf.htm.
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I think the symptoms are too regular for a disease. In other words the signs of a disease would be at random. It is probably a mineral deficiency which has lead to necroses at the leaf edge.
Perhaps it is leaf scorch as Jth suggests. I will do some looking!
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I dont believe that this is a fungus - the typical nerium fungi are ascochyta, sometimes septoria and beside that several bacterioses. I cultivate nearly 60 varieties of nerium and I am nearly sure, that your symptoms are NOT fungi.
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Nigel please read this website , it may give you some ideas since the symptoms are not that apparent
http://hortipm.tamu.edu/ipmguide/nutrient/diagnosi.html
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Very interesting David, thanks I am saving the link. I take the opportunity to share a chart I found about last week only, which sums up nicely the interaction between soil acidity and nutrients availability. joe
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Do we know the pH of Nigel`s soil.?
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Only just looked at these.
To me the top photo shows just normal changes in leaves as they get old and die (it seems to be the leaves farthest down the stems that are affected). As the leaves become yellow, defects stand out more, and of course being the oldest leaves they are most likely to have accumulated bruises, nibblings, etc. - all adding to the appearance of disease.
Is the bottom one actually a Nerium? It looks more like a Myoporum laetum to me.
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Dear Maria Sansoni is there a particular variety of Nerium that has a strong scent? ??? Very rarely I cross N. oleander plants that do diffuse a lovely scent to say 20-50m. One I remember was a dark-pink double-form. Thank you
:)
re. nutrient deficiency... reading David's link carefully, it looks like the plant in 2nd photo suffers from (P) and (K)...
At any rate, the deficiency is from any of the nutrients that get around easily around the plant, which shows first in older leaves, ie N, K, P, Mg, Zn & Mo.
what do you say? Where is Nigel?!
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I agree with you Mike, the second photo is definitely Myoporum laetum. I'm looking at mine now and it has exactly the same yellowing which I put down to it feeling a bit tired and stressed.
GIJoe, a quick sniffing survey of the many and various oleander in my garden has revealed that only the double forms have a sweet scent and they are all pink, both medium and dark. The problem is that the flowerheads get so heavy that they keel over. Here in Greece I buy oleanders when they're in flower so that I know what I'm getting - no named varieties. I keep the summer-bought plants in my nursery, which is watered daily, until the autumn. Oleanders have no problem with drought or flood. I also take cuttings from plants I admire along the road.
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Dear Fleur, so you observed the same with double-forms. Exactly, the one that I always notices is on Spetses island, right outside Klimis café. Oleanders are all hightly toxic, but I suppose sniffing is not dangerous.
They are planted here (Attica, Greece) everywhere lately, and allowed to coppice unchecked. Yes, I definitely prefer this scented double-form, especially if diligently pruned to form a multi-trunc small tree.
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Re the weighing down of branches by the heavy double flowers...
Maybe they could be planted on the side of a bank, so the wind and light bias might induce the stems to lean away from the bank. Then, when the flowers come, the branches would all arch over the same way, and they'd have much more height to work with - so they wouldn't reach the ground.
Very crudely, I have in mind an effect like you get with Russelia.
Just a thought.
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Mike, yes for a bushy effect you mean? I am relieved to see you are not advocating using a helicopter again hehe (like for Duncan's Bamboo ;)
It's a fantastical plant for mediterranean gardens, isn't it?... putting aside its toxicity and the fact that is being overplanted lately, in Athens for example.
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Yes, it really is a good plant for med. gardens. But its toxicity does worry me now and then. I worry not so much about people burning prunings, but more about the smoke should a bush fire sweep through a planting.
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Mike, I would not worry about the toxicity of oleander fumes, as far as I know it is only toxic if ingested in sufficiently high doses (don't feed your horse with this, though). It has been used in folk medicine for more than 1500 years, it has a narrow therapeutic index, but it has been approved by the USFDA for cancer treatment, and topical application for various skin diseases has been shown to be safe.
I am very fond of oleanders and have a few in my garden in Greece. It took a long time before they finally decided to survive, but those with double flowers and the nice scent are the ones that have grown the most.
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Where is Nigel , there are 3 or 4 questions outstanding??
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Jorun - re smoke...
Thanks for your comments. I appreciate your academic credentials.
I find many reports of problems with Oleander smoke. Some of them are spurious, true. But some seem legitimate, eg.
"...inhalation of oleander smoke or ingestion of oleander can result in toxicity to humans or animals and potentially lead to death (Langford & Boor, 1995)." referring to
Langford, L. D., & Boor, P. J. (1996). 'Oleander toxicity: an examination of human and animal toxic exposures' Toxicology, 109, 1-13.
[ http://chemweb.calpoly.edu/cbailey/377/PapersW08/HollyM/home.html ]
--and--
"Toxicity issues of smoke from the Anacardiaceae family and the Oleander are discussed..."
FIRE TECHNOLOGY, Volume 36, Number 3 (2000), 163-183, DOI: 10.1023/A:1015462710856
'Fire and Pesticides, A Review and Analysis of Recent Work'
[ http://www.springerlink.com/content/a80dbrxr8bvyd0cb/ ]
--and--
"The smoke from burning oleanders is especially toxic. Earlier this year, a fire occurred in a Phoenix neighborhood and the fire department called for an evacuation of the area until the fire was under control, all because of the burning oleander."
[ http://waterwhendry.blogspot.com/2007/08/nerium-oleander-vulnerable-after-all.html ]
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Dear All,
Some of my white oleanders are also suffering like yours Mike, particularly after the long summer with no rain. I suspect they have the disease which seems to be around here in Provence. Does any one know if giving them some fertiliser would help now the rains are coming?
Thanks also to the forum members for confirming my suspicion that only double flowered Oleanders are perfumed.
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Having just seen this I think that both the Nerium and the Myoporum are just stressed. The Nerium is probably short of sufficient moisture. I have seen similar stress in plants in the wild in NE Crete growing in seasonally dry gullies and stunted to less than 1 meter high.