FACTSHEET
Exotic Pest Alert: Fire blight
Plant Biosecurity Orange
Erwinia amylovora is an exotic plant pest
causing fire blight
Fire blight is a serious threat to Australia’s
apple and pear industry
If symptoms are seen it must be reported
promptly to the Exotic Plant Pest Hotline
1800 084 881
Symptoms
Fire blight is a bacterial disease caused by
Erwinia amylovora.
Fire blight can appear as different symptoms,
depending on which plant parts are affected and
seasonal timing. The most typical symptom is the
shepherd’s crook (Figure 1).
Figure 1 Typical shepherd’s crook symptom of fire blight
Blossom blight
The first symptoms of fire blight can be seen in the
flowers as blossom blight (Figure 2). In the early
stages of infection blossoms appear water-soaked
and gray-green but quickly turn brown or black.
Generally the entire flower cluster becomes
blighted and killed. Bacteria move from the flowers
into the shoots.
Shoot blight
Shoot blight is the most obvious symptom of fire
blight and can appear one to several weeks after
petal fall. The leaves and the stem on young shoot
tips turn brown or black and bend over into a
characteristic shape similar to the top of a
shepherd’s crook or candy cane (Figure 1).
Small droplets of sticky bacterial ooze can often be
seen on the surface of fire blight shoots when the
weather is warm and humid.
Under favourable conditions shoot blight infections
will multiply and continue to expand down the
stems. When the bacteria invade and kill the
cambium tissue of the branch, all flowers, leaves
and fruit above the girdled area die.
Figure 2 Fire blight in apple blossom and leaves
Infected trees appear to be scorched by fire, hence
the name ‘fire blight’.
Shoot blight infections can expand beyond the
current season’s growth into the older supporting
wood, causing dark sunken cankers to form.
February 2012, http://www.dpi.nsw.gov.au/factsheets for updates
Primefact 1161 first edition
Plant Biosecurity
Fruit blight
Canker blight
Fruit appears small, dark and shriveled if infected
when young (Figure 3). If infected later expanding
red, brown or black lesions appear.
Cankers on branches or stems appear as dark
discoloured slightly sunken areas (Figure 4) with a
narrow callus ridge along the outer edge.
Infected fruit often exudes droplets of sticky
bacterial ooze especially when the weather is
warm and humid.
The inner bark under the bark associated with a
canker may change colour from green to brown
depending on the host plant variety.
Infected fruit gradually dries and remains attached
to the branch rather than dropping.
Active cankers produce bacterial ooze.
Rootstock blight
The entire tree on a susceptible rootstock can wilt
and die if these areas become infected.
Lifecycle
Fire blight bacteria overwinter in blighted branches
and at the edge of cankers formed during the
previous growing season (Figure 5).
As the weather warms in spring the bacteria
multiply and ooze to the surface in sticky droplets.
Bacteria can be transferred from the active cankers
to spring blossoms by insects and rain splash.
Figure 3 Fire blight symptoms on young apple fruit
Once in the flowers the bacteria multiply rapidly
and when temperatures are greater than 18 oC can
build to very high levels. Bacteria can be moved
from flower to flower by bees.
Infection does not usually occur unless the
bacteria are washed by rain to natural openings at
the base of the flower.
Blossoms wilt and die about 1-2 weeks later.
Bacteria oozing from blossoms spreads to young
green shoots.
Figure 4 Early signs of fire blight on apple shoot
As the season continues and shoot growth slows
and stops the shoots become progressively less
susceptible to new infections. The rate at which
bacteria move through woody tissues also slows
down and cankers are formed.
Spread and movement
Insects and rain move the bacteria to flowers and
shoots. Infection occurs through wounds caused
by insects feeding, wind-whipping and hail. Within
the growing season bacterial ooze is produced
from these new infection sites.
Further spread occurs as long as shoots keep
growing and wounding of the tree occurs.
Hosts
Figure 5 Older fire blight canker on apple tree
p 2 Exotic Pest Alert: Fire blight
A wide range of plants in the Rosaceae (rose)
family are affected by fire blight.
Fire blight hosts include fruit trees such as apple,
pear and quince and amenity plants such as
cotoneaster, crab apple, flowering quince and
hawthorn.
Resources
APAL (2001) Fire Blight Prevention and Management
“Orchard Best Practice”
Colorado State University Extension Fact Sheet
No. 2.907 ‘Fire Blight’
World distribution
Fire blight was first recorded in the USA in 1794 on
apples in New York State. The bacterium is native
to North America and is present throughout the
continent where susceptible plants of the
Roseaceae family are grown.
Cornell Cooperative Extension (1994) Tree Fruit Crops
IPM Disease Identification Sheet No. D3 (revised)
‘Fire Blight’
Washington State University Extension Chelan-Douglas
County Fact Sheet ‘Fire blight management in the
Pacific Northwest USA’
Fire blight is present in many regions of
commercial apple and pear production.
Figure 1 courtesy of David Pickering Department of
Primary Industries New South Wales
Fire blight is not present in Australia.
Figure 2 courtesy of K.D. Hickey, Cornell
International experience
Figure 3 courtesy of Clemson University - USDA
Cooperative Extension Slide Series, Bugwood.org
There is no cure for fire blight.
Prevention is the best option for the management
of fire blight.
Figure 4 courtesy of William M. Ciesla, Forest Health
Management International, Bugwood.org
Figure 5 courtesy of Christine Horlock ,
Biosecurity Queensland
Actions to minimise risks
Put in place sound crop hygiene including:
•
on-farm biosecurity to prevent entry,
establishment and spread of pests and
diseases
•
ensure all staff and visitors are instructed
in and adhere to on-farm hygiene practices
•
regularly monitor your crop
•
keep records
Reporting
If you suspect symptoms of fire blight:
Call the Exotic Plant Pest Hotline on
1800 084 881
© State of New South Wales through Department of Trade and
Investment, Regional Infrastructure and Services 2012. You
may copy, distribute and otherwise freely deal with this
publication for any purpose, provided that you attribute the
Department of Trade and Investment, Regional Infrastructure
and Services as the owner.
ISSN 1832-6668
Disclaimer: The information contained in this publication is
based on knowledge and understanding at the time of writing
(February 2012). However, because of advances in knowledge,
users are reminded of the need to ensure that information upon
which they rely is up to date and to check currency of the
information with the appropriate officer of the Department of
Primary Industries or the user’s independent adviser.
Published by the Department of Primary Industries, a part of the
Department of Trade and Investment, Regional Infrastructure
and Services.
PUB12/33
Take photos not samples to minimise the risk
of spreading the disease
Contact your local district horticulturalist
Visit the Plant Biosecurity website for further
information
www.dpi.nsw.gov.au/biosecurity/plant
An exotic plant pest is a disease causing organism
or invertebrate not present in Australia and which
threatens agricultural production, forestry or native
and amenity plants.
Exotic Pest Alert: Fire blight p 3