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Q: Olive tree disease treatments ( Answered 4 out of 5 stars,   1 Comment )
Subject: Olive tree disease treatments
Category: Miscellaneous
Asked by: thankyou1234-ga
List Price: $100.00
Posted: 10 Aug 2006 13:10 PDT
Expires: 09 Sep 2006 13:10 PDT
Question ID: 754744
What are the names and treatments of possible olive tree diseases with
the following symptoms:
1. Branches have slight swelling and brown (dead) leaves near tips
(last 6"), sporadically throughout tree.
    Type of tree: Sevillano, age estimated at 50-60 years; height
approximately 20'; location San Francisco.
2. Large limbs have large damp areas of bark 6-12" in diameter
(discolored/black). Leaves normal.
    Type of tree: Mission, age estimated at 50-60 years; height
appromimately 30'; location San Francisco.

Request for Question Clarification by boquinha-ga on 11 Aug 2006 09:49 PDT
Hello thankyou1234-ga,

I have spoken to my mother-in-law who is an expert gardener in the Bay
Area. She has some ideas of what the problems could be, but says it
would be very helpful to know in which county you live. Once I have
that information I can continue with the research. I've already got
quite a bit of information about possibilities and am composing an
answer that I'm sure will be useful to you.

Subject: Re: Olive tree disease treatments
Answered By: boquinha-ga on 14 Aug 2006 12:11 PDT
Rated:4 out of 5 stars
Hello thankyou1234-ga!

I saw your question and immediately knew that my mother-in-law, a
graduate of the University of California?Davis Master Gardener program
could help you. The fact that you are in California yourself makes
this even better. She was able to give me some leads on information
that should help you, as well as more resources you may want to use.
Here is what I?ve found.

- - - - - - - - - - - - - - - - - - - -


According to the Master Gardener, the most likely problem for tree #1
is verticillium wilt. This is caused by a fungus and can be confirmed
by taking an affected branch and peeling back some of the bark. If you
see dark stains that run along the grain, this is your culprit. Here
are some other points to understand about it:

* Caused by a soil borne fungus 
* Leaves on branches die with the onset of warm summer weather. 
* Trees die after repeated attacks over several years. 
* Infection usually occurs in cool moist soil in late winter and spring. 
* No reliable methods of control have been developed. 
* Fumigation may be successful. 

She says that olive trees do well with pruning so you can prune out
and dispose of the problematic branches. This is assuming that there
are not an inordinate number of damaged branches. This is really the
only treatment that will work consistently. Once you?ve pruned the
tree, be sure to clean your tools with a mild bleach solution to
prevent spreading the fungus to other plants and trees. Any clothing,
including shoes or boots that come into contact with the affected tree
branches can also be a means of spreading the fungus so be aware.

The Master Gardener also mentioned the website as a good resource for olive growers. It
contains information about verticillium wilt, among other problems.

?Verticillium wilt fungus is a sneaky disease, entering a plant
through the roots in the soil.  Infections are not obvious like some
other diseases, such as powdery mildew or sycamore blight.  Symptoms
can be acute, with leaf curling and drying, abnormal red and yellow
coloring of the leaves, partial defoliation, wilting and dieback of
branches.  This wilting and dieback will typically develop on one main
branch, a sector of the crown, or an entire side of the tree.  Chronic
symptoms are stunted growth, yellowish leaves, crispy brown edges on
the leaves, slow and stunted growth, heavy seed crops, and branch

Trees with verticillium wilt may limp along for years, exhibiting
symptoms some years and other years not showing up at all.  However,
the disease can suddenly attack a completely healthy tree causing it
to wilt and die in a short period of time.

The first outward symptoms of verticillium wilt are leaf scorch,
abnormal coloring, and dieback of branches.  However, there are many
things that cause the same symptoms.  Girdling and encircling roots,
root and crown rot, drought stress, compacted soil, trunk injury, and
improper planting can all cause similar symptoms.?

?Signs of verticillium wilt include new leaves rolling inwards and
losing their deep-green, waxy luster and becoming dull gray and brown.
Leaf-drop and twig die-back may follow, depending on the severity of
the infection. Tree death rarely occurs, rather portions of the tree
will die and then new growth may develop from dead areas. The only way
to control this disease it to plant resistant varieties of olive such
as Oblonga. . . .

Infected plants will suddenly wilt during the summer when temperatures
are high. Dead or dying foliage will remain attached to the plant and
the roots of the plant become rotted and brown in color.?

?In California, verticillium wilt is a serious fungal disease. There
is no effective treatment other than avoiding planting on infested
soils and removing damaged trees and branches. A bacterial disease
known as olive knot is spread by pruning with infected tools during
rainy months.?

Two other possibilities are Peacock Spot and Cercospora. By the
descriptions you?ve given these are a bit more unlikely, but you can
compare your trees to photos and see for yourself in order to be sure.
These are both diseases of the leaves caused by fungi. Peacock Spot
occurs after particularly heavy rainfall in fall, winter, and spring.
It causes dark spots with halos on the underside of the leaves.
Cercospora usually occurs in the northern coastal areas of California
and produces a ?sooty mold?-like appearance on the leaves. The leaves
then turn a yellowish color and fall off. For pictures and a more
thorough description, see this publication from UC Davis.

- - - - - - - - - - - - - - - - - - - -


Your second tree presents a bit of a diagnostic problem. There is no
one pest or disease that seems to fit exactly the description you?ve
provided. The olive tree usually prefers a dry, hot climate, which is
why they normally do so well in Northern and Central California. On
this one, the Master Gardner said that the winter rains were so heavy
this year that there may be a number of problems popping up in the
olive orchards.

Here is a list of potential pests (along with treatments when
available) common to the olive tree from the website I?ve mentioned some of them before.

*Nematodes (fumigation before planting will reduce the incidence of attack)
*Olive knot (Copper containing fungicides applied to wounds and scars
are effective)
*Peacock Spot (Infected trees should be sprayed with copper-containing
fungicide in late autumn)
*Phytophthora (Water management is the basis for control)
*Verticillium Wilt (No reliable methods of control have been developed)
*Olive Moth (Controlled by good orchard management and natural
antagonists, or organic phosphate insecticides on first generation)
*Olive Shoot Moth (Controlled with appropriate insecticides)
*Olive Lace Bug (Chemical control with appropriate systemic insecticide)
*Black Scale (Petroleum sprays can be used and are most effective
against larvae, usually in late December and March/April)
*Olive Scale (Control similar to Black Scale)
*Circulio (Control includes barriers to stop beetles from climbing the
trunk or chemical control using appropriate pyrethroid)

Tuberculosis of the olive tree is another disease caused by a number
of bacteria. Typically it causes ?galls? or dark-colored swellings on
the branches that are somewhat smaller than what you?ve described.
Atypical cases do exist, however.

Armillaria Root Rot (Oak Root Fungus) is a disease that can cause
discoloration on the surface of the tree. It is usually confined to
the roots, but as it spreads, the discoloration may appear higher up
on the tree.

?Infected trees have slowly thinning canopies and appear weak. This
symptom often develops first on one side of the tree and then
progresses over several years to involve the whole tree. The bark and
outer wood of the upper roots and crown show discoloration.?

Here is another site with information on numerous pests and diseases
of the olive tree. It includes some articles on eradication as well.

- - - - - - - - - - - - - - - - - - - -


The University of California Botanical Gardens in Berkeley has a ?sick
plant? diagnostic clinic held on the first Saturday of most months.
You can take a portion of your trees to the clinic, with or without
additional photos, and an expert can help determine what the exact
problem is. You can contact them at (510) 643-2755 for specifics
regarding dates and times.

- - - - - - - - - - - - - - - - - - - -


Master Gardeners are available in most California counties to answer
any gardening questions you may have. For links to information on
Master Gardeners in the various California counties see Each county?s Master Gardener should
be knowledgeable about not only general gardening, but also
information specific to that county. Here is a list of contact
information for the various Bay Area counties.

= = = = = = = = = =
(510) 639-1275

= = = = = = = = = =
(925) 646-6586

= = = = = = = = = =

You can contact the Master Gardeners in Marin County through the
following email address.

= = = = = = = = = =

Merced County uses the Fresno county Master Gardeners. You can contact them at:
(559) 456-7563

= = = = = = = = = =
(707) 253-4221

You can also take a sample of your tree to the UC Cooperative
Extension at 1710 Soscol Avenue, Suite 4 in Napa. They are available
Monday, Wednesday, and Friday from 9am to 12 noon.

= = = = = = = = = =
(916) 875-6913

= = = = = = = = = =

Call the county offices and ask about Master Gardeners in San Joaquin County.
(209) 468-2085

= = = = = = = = = =
650-726-9059 x 109

For an online submission form see:

= = = = = = = = = =
(408) 282-3105

= = = = = = = = = =
(831) 763-8040

= = = = = = = = = =
(707) 784-1322

= = = = = = = = = =
(707) 565-2608

= = = = = = = = = =

Stanislaus County has a Tree and Vine Pest Hotline. This would be a
good place to start.
(209) 525-6841

= = = = = = = = = =
(530) 666-8737

In Yolo County, Master Gardeners are also available at the Davis and
Capay Valley Regional Farmers? Markets. For information on location
and times see:'s_Market.htm

- - - - - - - - - - - - - - - - - - - -

I hope that you find this information useful and I hope that you can
effectively nurse your trees back to health! If you have any need of
further clarification, please let me know how I can help.


Search strategy:

Discussing your question with a Master Gardener in the Bay Area
Online search

Search terms:

olea europaea disease California
"olive tree" disease California
common [pests OR diseases] "olive tree"
common [pests OR diseases] "olive tree" California

Request for Answer Clarification by thankyou1234-ga on 25 Aug 2006 13:39 PDT
Hi boquinha-ga:

In answer to your request for additional information, the trees are in
Marin County, within 100' of the Bay, but not in an area that gets

Clarification of Answer by boquinha-ga on 28 Aug 2006 14:11 PDT
Hello again thankyou1234-ga!

Living in Marin County, you can email the Master Gardeners at They will then be able to best assist you based
upon the most current information in your county. And the Diagnostic
Clinic at the UC Berkeley Botanical Gardens is still an excellent
resource for in-person assistance.

Thanks for posting your county?that helps me give you specific Master
Gardener contact information. As for everything else, the information
I?ve provided in my answer should still prove useful to you.

thankyou1234-ga rated this answer:4 out of 5 stars
Generally a good answer, but much of the information could probably be
found through other sources. The answer to part 2 of the question did
not appear to be correct, so we retained an arborist who solved the

Subject: Re: Olive tree disease treatments
From: boquinha-ga on 25 Sep 2006 13:43 PDT
Thank you for rating my answer. I'm glad your tree problem was resolved. 


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