The MGS Forum
Gardening in mediterranean climates => General Cultivation => Topic started by: Alisdair on September 23, 2011, 09:02:15 AM
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David Bracey has asked me to post this email which he had from MGS member Richard Kellner, who gardens on the island of Milos in the Greek Cyclades, with the attached pictures. I'm posting it here under cultivation as it looks to me as if no pest or disease is involved: given the exposure, I suspected salt damage, but in any event would think that a more sheltered position might help. Advice please!
I should be most grateful if you or one of your colleagues in the MGS could give me some advice regarding a Bay Tree which is not very happy. The tree, or rather bush, is in very poor earth ( containing a lot of rubble) and is very exposed to strong south and west winds, particularly in the winter. I attach some photographs which show that some of the leaves are yellowing and going brown especially in the lower part of the bush. New growth is emerging from the bottom of the bush. Is there anything I can do which would improve the plant's prospects!?
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My experience of native Laurus nobilis on Crete is that they only grow in very sheltered valleys where they achieve heights of around 20 m. With a girth of around 50 cm. Real exposure to salt winds would prevent this sort of growth but as long as they survive you will presumably get seasonal regrowth and therefor leaves to use.
From the first picture I would also say it looks as if you have some scale insects as well.
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It looks to me as though the brown leaves are the old ones - which suggest they are being discarded naturally. In that case, they should fall off due to natural abcission. If they stay attached, that's not such good news.
I agree the situation (salt in the wind, poor soil) may be hampering its health.
But the fact that it is shooting from the base is a good sign; a sign that at least the roots are OK.
Die back of parts of the top growth can be due to various disorders, such as bark damage (perhaps not obvious) and stem borers, but I don't see anything in the photos that suggests those problems.
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John, from the higher-definition original of the first picture I thought the scale insect presence, if any, was so slight that it couldn't be responsible for the browning :)
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I have a laurel that was just like Richard's until this summer, small and stunted, many brown leaves, it hardly grew at all. The soil is poor, rocks and clay, and it is exposed to wind from the north, east and west, no salt, spray, though. I must have had it for 10 years, suddenly this summer it started to grow, without any intervention from me, and looks very healthy, so maybe his tree will wake up one day as well, like mine. There are many big laurels around here.
The second of the photos do show quite a few scale insects (Coccus hesperidum), though, as far as I can see, they are hard to get rid of.
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If it is scale, and I think it, is then Richard has a job on his hands. In the good old days the amatuer gardener could buy an insecticide formulated to specifically control scales. They often contained an organophosphate insecticides plus mineral oil. To-day mineral oils or soap solution are the major weapons for the amateur.
Scales are sedentary "aphids" that is sedentary insects which suck sap and are protected from dessication by hard or soft scale on the outside of the body. Young nymphs crawl from the adult scale to infest new growth. Control is by suffocation , hence soap suds or mineral oil. I know members of the MGS Catalonian branch buy scalicides from their local co-operative. These are normally reserved for professional growers and are based on a group of chemicals known as neonicotnoids.
Richard should try to prune out infested branches and try to encourage new growth which also has to be protected. If it were salt damage you would expect to see heavier leaf scorching on the seawardside, however the damage appears to be at random across the tree.
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In my opinion, it IS the scale, there is a lot, look at the bark. They can kill a bay, specially it is is weakened by other factors, having to stand strong winds, in such an unfavourable position: that cement on the roots makes it very difficult to fertilize it, the plant can hardly absorb water, and the roots get probably baked in the summer- there is little or no air exchange at soil level, and too much air on the crown.
I would go with mineral oil, now, and given that the plant is so small I woult try to brush clean the bark with a softish brush, to get rid of hidden scale insects. But I would also try to improve the growth condition, opening the cement paving at the base, and adding mulch or, better, spent dung. That Laurel is starving. A well nourished plant is less prone to scale attacks. Eventually I would get rid of the upper trunk and let the lower growth take over.
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I have noticed on numerous occasions that trees/shrubs planted in my environment (naturally very rocky alkaline sub soil) take AT LEAST 3 if not 4 years to start to show good healthy growth. They only 'survive' for this time and then IF they are lucky enough to get their roots down between the rocks they then start to show their mettle. This scenario is not obviously not with all shrubs/trees but many do have this problem. We have a Laurus nobilis that looked, I would say, not 100% for 3/4 years and now it looks really well. I put this down to it now finding its way down amongst the rocks. However, I do worry about planting in concrete, stones and in what are called 'mediterranean' conditions, I am sure poisons emanate from these often unnatural and contrived locations and don't help the plant growth. In my view, beautiful as they may be for us to look at they simply are not in the main conducive to healthy plant life.
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I agree with Alessandra, it looks as if the scale insect is the culprit here, at least two potted bay trees I had here in Norway have been killed by the same. But like Pamela, I have also experienced that most of my trees and bushes have been struggling the first years (some times quite a few years) in Greece, my conditions are difficult, but if they survive that period, then they will be OK. I don't think poisons are causing the problems where I am, just poor, rocky soil and little water.
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I quite agree with both Jorun and Pamela with their comments about trees/shrubs taking several years to establish well in rocky soil. Even if you excavate a large, deep planting hole one never knows exactly what is lurking just below the point you stop. This is of course one of the big challenges when gardening in many Mediterranean areas. About 6/7 years ago I planted a Bay hedge to shield two large, above ground water containers that collect rain water from the roof of the house. One end of it grew away quite quickly with the first two plants far stronger than any of the others whilst the other end still looks sickly in comparison. I have made use of the nearby water supply to try to strengthen the weaker plants but it has made little difference and so I am sure there is a seam of rock beneath them that peters out towards the other end. This year has seen a slight improvement and so I am still hopeful that it will be OK in the end.
Over the years I have noticed that things will flourish in one place and look decidedly sickly in others. Usually I just move things around until they look happier but the real problem comes when you want a certain subject in a certain place as a focal point for example........
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With these sort of 'establishment' problems, especially in mineral soils (as opposed to organic ones) I sometimes find myself wondering about mycorrhizal associations. I have not researched this area enough. But I suspect that as seedlings germinate and gradually establish, they may acquire a fungal partner in the soil (possibly from the seed coat), and thereafter the two can develop in a balanced fashion. (You wouldn't see much of seedlings that failed to develop this beneficial association.) But if you transplant with reduced roots into a poor soil or rocky substrate, even if the mycorrhizae are still present, the balance may be lost, and take some while to recover.
Yes, the mycorrhizal factor may be lost in a general perception of the plant taking time to re-establish. I am just saying it could be a factor. And if it is, maybe mycorrhizal innoculation could help. This page gives a good introduction to that subject - http://www.ecotreecare.co.uk/mycorrhizal-inoculation-biology.htm (http://www.ecotreecare.co.uk/mycorrhizal-inoculation-biology.htm).
That is a general comment.
With respect to Laurus nobilis in particulat, I have no idea if mycorrhizae are relevant or significant.
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Mike the Scientific Committee did some trials in 2010 with a mycorrhizal preparation. I attach the conclusions:
"Conclusion: This trial indicates a small 5-10% yield increase for mâche grown under winter conditions; further studies would be required to confirm this result on different species of mediterranean plants grown under spring or summer conditions and over a longer period. " for your perusal!
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Interesting David, thanks.