The MGS Forum
Gardening in mediterranean climates => Pests and diseases => Topic started by: MikeHardman on August 02, 2011, 09:03:28 AM
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I have a small border between a shingled parking area and the top of a steep bank of soil (covered with old grasses now). I planted it all at the same time, with the same plants from right to left: Aptenia cordifolia cuttings and Nerium oleander as small potted plants. At one end, both types of plant are doing very well (dark green, spreading and growing well), in the middle they are not so good (leaves a little yellow, less growth), and at the other end, they leaves are very yellow on the Aptenias and growth stunted.
Irrigation is similar throughout.
All the soil was put in place at the same time, raising the level somewhat (new soil deeper at the good end).
The good end also gets a little shade from a small wall.
The poor end is closer to a Myoporum laetum shrub and cypress trees (Cupressus sempervirens var. sempervirens; not fastigiate) (allelopathy issue?)
Any thoughts?
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Nematodpathy? An immediate examination of the roots is crucial
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Ooh.
Don't want that!
Would I be looking for nematodes visible with a hand lens, or do I have to get my microscope out?
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If they are in the soil a simple inspection will prove the case as the roots will look deformed by evident tumors.
If they are leaf nematodes they will have to be seen in a lab. In any case, a general alarm is expected.
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Thank you ezeiza.
The weak plants have all improved: they are greener and they have produced some new shoots and leaves. So I don't want to disturb them now!
But I excavated by one, and found the roots were in good condition - smooth and cream-coloured.
The new leaves, too, look fine now. Even the ones that didn't, which are still pale, are robust.
So I'm keeping my fingers crossed that the worst is over, and that they will continue to gain strength.
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Hmmmmm......
Do you have a female dog?
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no - no dog (and none that come through the garden); thanks for the thought
Here are a couple of photos to show progress of these particular plants (compare with earlier photos).
The greenest patch has continued to expand; I have to cut it back once a week, providing lots of useful cuttings. The other patches are less yellow and have made new growth, just not as fast.
The whole area gets a similar watering regime and has had no fertilizer.
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I'm emailing the RHS advisory service, to pick their brains and referring them to this topic...
For that purpose, I'm adding a few photos of the bewitched border as it is today, partly in the hope that this documentation may be a stepping stone on the way to explanation of the problem and later resurrection of the border.
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Mike what about root competition. Those Cupressus must have roots growing somewhere.
What is the black snake in the bed???????????????? David
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David,
The imported soil gives about 15cm of extra soil depth, which I am sure the Cupressus roots won't have invaded yet (they were below the old soil surface). Yet, small plants within that depth are affected. And they have had irrigation during the summer. So I don't think the Cupressus are the problem in terms of pure competition. Modes of operation of allelopathy leave a window of possibility, however (eg. root gases/exudates?)
The black snake is irrigation pipe; you knew that!
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I think David might perhaps be on to something Mike, even with your irrigation. Though your plants will no doubt love that 15cm of added topsoil, it may be the moisture content of what's underneath it that is the dominant factor.
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Thanks for that thought, Alisdair; it is a possibility.
I have lots of self-sown Sinapsis seedlings, and some rooted-in-water Aptenia cuttings. Both plants are growing well at the moment, and I know exactly what shade of green is normal. I'll use those to do some experiments, planting them in the problem soil both in situ and in pots. I will also transpose good/problem soil in the planting scheme. The soil in the border is saturated at the moment despite the Cupressus, so deep dryness should not be an issue. That means that, if all the plants grow OK, the culprit must be a Cupressus-related factor, such as deep dryness or seasonal allelopathy (not a soil or location problem).
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re
If they are in the soil a simple inspection will prove the case as the roots will look deformed by evident tumors.
If they are leaf nematodes they will have to be seen in a lab. In any case, a general alarm is expected.
Just by way of a slight update:
The one Aptenia plant on which I have seen deformed roots, was one of the strongest-growing. It had got its roots down below competing Cypress roots, but they had distinct swellings. I'm not sure what to make of them. Perhaps they are nitrogenic bacteria nodules? But I have not heard of them in association with Aptenia.
Note: The root had been out of the ground for about a week when I photographed it, so it is a little shrivelled.