This document discusses diseases that affect olive trees. It describes 8 key diseases: Botryosphaeria Blight, Mycocentrospora, Olive Knot, Peacock Spot, Phytophthora Root and Crown Rot, Verticillium Wilt, and Armillaria Root Rot. For each disease, it provides details on the pathogen, symptoms, signs, environmental conditions needed for disease development, and management strategies. Common management approaches include pruning, irrigation management, and applying preventative fungicide treatments.

1. By Muhammad Usman Arshad
(Internee at Barani Agriculture
Research Institute, Chakwal)

2. Olive
Introduction:
The olive, known by the botanical name Olean
Europaea, meaning "European olive", is a species of
small tree in the family Oleaceae.
The olive tree, Olea Europaea, is an evergreen tree or
shrub native, to the Mediterranean, Asia and Africa.
 It is short, squat and rarely exceeds 8-15 m in height.

3. The silvery green leaves are oblong, measuring 4-10 cm
(1.6-3.9 inch) long and 1-3 cm (0.39-1.18 inch) wide.
The fruit is a small drupe 1-2.5 cm (0.39-0.98 inch)
long, thinner-fleshed and smaller in wild plants than
in orchard cultivars.
Olives are harvested in the green to purple stage.

4. Diseases of Olive
 Botryospaeria Blight
 Mycocentrospora
 Olive Knot
 Peacock Spot
 Phytophthora Root & Crown Root
 Verticillium Wilt
 Armillaria Root Rot
http://ipm.ucanr.edu/PMG/selectnewpest.olives.html

5. Botryosphaeria Blight
 PATHOGEN: BOTRYOSPHAERIA DOTHIDEA
 SYMPTOMS AND SIGNS
 The pathogen enters through wounds or tissue infected,
invades the branch, forming an elliptical canker.
 This canker can girdle and subsequently kill small
shoots and branches.

6.  Sources of inoculum for this disease are rachises,
shoots, and petioles killed by B. dothidea during the
previous growing season.
 Cankers can also provide inoculum for as long as 6
years.
 Cankers caused by the genus Botryosphaeria can
colonize the vascular tissue very fast, it is critical to
manage the disease properly.

7. Management
 Proper orchard sanitation, pruning, and irrigation
management can be helpful in managing this diseases.
 The best approach to reduce both the disease level and
production of inoculum within olive orchards is a
combination of proper orchard sanitation, pruning,
and irrigation management.
http://ipm.ucanr.edu/PMG/r583100511.html

8. Mycocentrospora
 Pathogen: Mycocentrospora cladosporioides
 SYMPTOMS AND SIGNS
 It causes the leaves to appear slightly chlorotic
(yellowing—some varieties show more chlorosis than
others). The undersides of some leaves become
discoloured

9.  High temperatures restrict spore germination and growth,
thus the disease is inactive during the warm, dry summers.
 MANAGEMENT
 In cool, wet areas, apply preventive treatments to olive trees
after harvest, but before winter rains begin and again in
spring, if rainy weather persists.
http://ipm.ucanr.edu/PMG/r583100411.html

10. Olive Knot
 Pathogen: Pseudomonas savastanoi
 SYMPTOMS AND SIGNS
 Olive knot appears as rough galls or swellings about 0.5
to 2 inches in diameter on twigs, branches, trunks,
roots, leaves, or peduncles (fruit stems).

11.  Olive knot can girdle and kill trees if infections occur
on the trunks of young trees.
 They are readily spread by water at all times of the
year. Bacteria survive in galls and as epiphytes on
leaves and twigs.

12.  MANAGEMENT
 It is also helpful to carefully prune during the dry season
(July to August) to remove galls on twigs and branches.
 Leaf scars are susceptible when fresh, time treatment to
protect as many leaf scars as possible.
 Harvest occurs in fall or winter when rain is likely.

13. Peacock Spot
 Pathogen: Spilocaea oleaginea
 SYMPTOMS AND SIGNS
 Peacock spot appears on leaves as sooty blotches that
develop into black, circular spots about 0.1 to 0.5 inch
(2.5–12 mm) in diameter.
 The optimum temperature is 58oF to 75oF.

14.  Twig death may occur as a result of defoliation.
 The margins of lesions enlarge in fall, and a new crop of
spores develops there.
 New infections are associated with rainfall and mostly
occur during fall and winter.

15.  MANAGEMENT
 If olive trees exhibit peacock spot leaf symptoms, it is
important to treat for it yearly.
 Apply a preventive treatment in late October before
winter rains begin, and again in the spring if wet
weather persists.

16. Phytophthora Root and Crown Rot
 Pathogen: Phytophthora citricola
 SYMPTOMS AND SIGNS
 The bark of the root crown turns dark
as the infection spreads.
 It requires free moisture in the soil to
produce and disperse swimming
zoospores.

17.  The pathogen can live independently in the soil and
survive long periods of dryness as oospores.
 MANAGEMENT
 Careful soil water management is the best foundation
for control of Phytophthora root and crown rot.
 Plant trees on berms, shorten irrigation times, and
improve soil water penetration and drainage.

18. Verticillium Wilt
 Pathogen: Verticillium dahliae
 SYMPTOMS AND SIGNS
 Symptoms of Verticillium wilt appear when leaves on
one or more branches of the tree suddenly wilt early in
the growing season.
 Darkening of xylem tissue, a key symptom for
distinguishing.

19.  The fungus survives from season to season in the soil
and probably in the roots of infected trees.
 Some trees recover naturally from an initial infection,
but others may die.
 This mostly depends on the strain of the fungus
(defoliating or non-defoliating), the resistance of the
cultivar, and the amount of inoculum in the soil.

20.  MANAGEMENT
 Inoculum levels can be reduced before planting by
flooding the fields during summer, growing several
seasons of grass cover crops.
 After trees have been planted, there is no reliable
method of control.
 Post plant soil solarization has provided inconsistent
control in established plantings.

21.  Soil Solarization
 Beginning in late spring, cover the surface of an entire
block with transparent plastic that has a UV-inhibitor
additive.
 Leave the plastic on throughout the summer and as long
as practical. Inferior plastic will break down and render
the treatment ineffective.
 Solarization gives inconsistent results when used in
replant spots.

22. Armillaria Root Rot
 Pathogen: Armillaria mellea
 SYMPTOMS AND SIGNS
 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.

23.  Roots infected with Armillaria mellea have white to
yellowish fan-shaped mycelial mats between the bark
and the wood.

24.  MANAGEMENT
 Armillaria root rot is most likely to be present in soils
where oak trees previously grew.
 No olive rootstocks are known to be resistant, and
infected trees cannot be cured.

25.  Although the research has not been conducted
on olive in this regard but there are some
techniques that can be applied such as-
 Remove soil from around the base of the tree to a
depth of 9-12 inches.
 Leave the trunk exposed and keep the upper roots and
crown area as dry as possible.

26.  During winter, provide drainage if necessary so that rain
doesn't collect in the hole.
 Recheck the hole every few years to make sure it has not
filled in with leaves, soil, and other matter; the hole must
be kept open and the crown and upper roots exposed.
http://ipm.ucanr.edu/PMG/r583100211.htm