The MGS Forum

Gardening in mediterranean climates => Pests and diseases => Topic started by: MikeHardman on December 26, 2018, 10:25:01 AM

Title: sickly olive
Post by: MikeHardman on December 26, 2018, 10:25:01 AM
I have 2 smallish olive trees, about 12 years old.
One is in good health - grey-green leaves all over.
The other is sickly - many leaves turning yellowish. But it is not the normal sequence of evergreen leaf yellowing: it is the younger leaves that are yellowing. And after yellowing, they drop off (usually without turning brown), leaving the ends of the twigs bare.

The hundreds of other olive trees in the area look fine; I have seen none showing symptoms similar to my sickly one.

Other plants growing nearby the sickly olive are OK (eg. a pomelo).
The tree produced fruit earlier in the year.

In earlier years, the tree had suffered from stem boring larvae (perhaps leopard moth, seen locally). Earlier in the year, small sprigs had their leaves turn brown, and there were minor signs of larval nibbling at the leaves. I snipped off those sprigs.
Perhaps either/both of those allowed infection to enter...

I wondered if it was Xylella fastidiosa (bacterial disease causing widespread devastation of olive groves in southern Europe, also called 'olive quick decline syndrome').
"The disease causes withering and desiccation of terminal shoots, distributed randomly at first but which then expands to the rest of the canopy"
In my case, I have not noticed 'desiccation of terminal shoots' as such - the twigs do not exhibit longitudinal shrinkage wrinkles. But maybe by 'desiccation' they mean defoliation?

I would be very grateful if anybody can tell me what is wrong!

1. healthy olive - all foliage grey-green
2. sickly olive - whole tree
3. sickly olive - close-up showing general yellowish demeanour
4. close-up of (3) - leaves grading from grey-green to yellowish towards tip
5. sickly olive - defoliated branch (with a greener branch behind it, confusingly)

Happy Christmas and New Year to everybody.
Title: Re: sickly olive
Post by: JTh on December 26, 2018, 03:45:39 PM
I really hope your olive tree is not infected with Xylella fastidiosa, that would be dreadful, but it does not sound likely if that's the only tree in your area that is suffering.

It seems as if nutritional deficiencies or waterlogged soil are the main reasons for yellowing leaves, and the most common symptom of calcium deficiency is chlorosis (leaves turn pale or yellow-white). Some years ago several of our olive trees were suffering from yellowing leaves and we were recommended to use fertiliser regularly (in winter), plus some borax every  few years; we have not had any problems since then.
Title: Re: sickly olive
Post by: MikeHardman on December 26, 2018, 04:46:46 PM
Hi Jorun,

Thanks for your thoughts.
My sickly olive is near the edge of a terrace, with a steep slope below. So it is not at much risk of water-logging. The fields down below are a different matter (see photo, 19dec18), but the olive trees down there are showing none of the symptoms of my sickly one.

However, in the autumn when the rains began (intermittently), I was still irrigating and this olive is on the same run as my citrus trees' irrigation. So it might have been getting some water. But not enough to stress the roots, IMO.

Reading-up on mineral deficiencies in olive, specifically
Joe Connell's presentation 'Olive Mineral Nutrition'
- the most common deficiencies are in N, K and Bo
  (in California at least, deficiencies in Zn, Ca, Mg, P, Cu, Fe, Mn, Mo are ~unknown)
- my tree is not showing classic symptoms of deficiency of K or Bo
- my tree might be showing signs of N deficiency
  (small and yellowish leaves,  poor shoot growth, sporadic bloom, poor fruit set)

This paper gives more detail on symptoms, some of which hint at a boron deficiency, viz.
"- Chlorosis (yellowing) and death of the growing points.
" - Trees suffering from boron deficiency appear chlorotic from a distance and delay entering the vegetative stage."
But my tree's leaves are yellowish all over; they don't show the classic brown tip and yellow band between the brown and green; nor the 'monkey-face' fruits.
I note with boron, that there is a risk of toxicity due to over-fertilization.

Title: Re: sickly olive
Post by: MikeHardman on February 06, 2019, 10:14:34 PM
Minor update:
- the tree seems to have stopped declining
- there are some new shoots showing fairly low-down
- I emailed Brian Chatterton, but I have not had a reply yet; maybe when he gets back from India... (Brian wrote an excellent article 'Pruning Olive Trees' in The Mediterranean Garden No.34 July 2003)

Title: Re: sickly olive
Post by: MikeHardman on March 31, 2019, 02:05:56 PM
Decline definitely reversed - quite a lot of new growth now, as per photos.
And the oldest leaves are turning distinctly yellow before falling off (good).
Title: Re: sickly olive
Post by: JTh on March 31, 2019, 02:45:48 PM
That definitely looks promising
Title: Re: sickly olive
Post by: MikeHardman on March 31, 2019, 09:45:59 PM
Yes, Jorun.
Of course, olives have remarkable abilities of resurrection after brutal transplanting even when mature. So I wonder what is happening under ground... Maybe it suffered some trauma last summer, then re-rooted, and we are now seeing signs of renewed vigour in the top growth as a result of that renewed root activity.