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Integrated Management of Fire Blight on Apple and Pear in Canada

What is fire blight?

Fire blight, caused by Erwinia amylovora, is a bacterial disease of apple, pear, hawthorn, crabapple and ornamentals in the Rosaceae family. The disease can result in the loss of branches and tree structure. In severe cases, when the bacteria progresses into the trunk or infects the rootstock, entire trees can be killed. The severity of disease is dependant on cultivar and rootstock susceptibility, general tree health, cultural practices and environmental conditions. Economic losses to fire blight occur due to a loss of fruit-bearing surface and tree mortality. Trees may need to be removed and replanted or, in severe cases, whole blocks of trees may need to be replaced.

What does fire blight look like?

The symptoms of fire blight depend on the part of the part of the tree that is attacked. Blossom blight (Figures 1 and 2) results in blackened/shrivelled blossom clusters. Shoot blight (Figures 3 and 4) is characterized by the typical 'shepherd's crook' symptom. Cankers (Figures 5, 6 and 7) form once fire blight progresses into larger branches, trunk and the rootstock. Cankers are typically smooth edged when first formed, but the margins become cracked and more pronounced with time. Infections can also be identified by the discharge of bacterial ooze from infected plant surfaces.

Where does fire blight come from?

Fire blight bacteria overwinter in cankers or strikes on host trees. In the spring, the bacteria can multiply very quickly, causing the surfaces of cankers to ooze bacteria. Bacteria are spread to blossoms by insects (for example flies, honeybees) and splashing rain. Rainfall, high relative humidity and/or dew allow the bacteria to travel into the stigma of flowers and into the tree. Blossom infections often result in shoot infections later in the season.

How do I save my trees once they are infected with fire blight?

There is no cure for fire blight, but the spread of bacteria can be limited by using sound pest management strategies in an integrated management program. Such a program should include diligent pruning to remove cankers in the winter, pruning during the growing season the removal of blight symptoms as they appear, a balanced nutrition program and the use of prediction models to determine appropriate timing for the application of control products to limit the spread of the disease.

How do I avoid problems with fire blight in the future?

Today, the trend is to plant higher density orchards with more valuable cultivars (many of which are highly susceptible to fire blight), making it difficult to avoid the disease all together. Risks can be minimized by selecting cultivars and rootstocks carefully when planting new orchards (a list of the susceptibility of some common cultivars and rootstocks is included in this publication). Sites chosen for orchards should have well drained soils with a pH between 5.5 and 6.5 and have adequate organic matter. The application of excess nitrogen should be avoided. An integrated pest management program for sucking-piercing insects (for example leafhoppers, aphids, plant bugs) should be implemented. An annual pruning program to remove as many fire blight cankers as possible is critical. The use of control products (copper or Bordeaux mixture before buds open, streptomycin for blossom blight control in combination with a prediction model to time bloom applications) will help limit disease spread. The use of Apogee® in mature bearing trees where blossom blight has been detected may help reduce susceptibility to the disease. With all the different factors involved in fire blight management, integrated pest management strategies are essential.

Methods for Fire Blight Management in Your Orchard

This factsheet contains information on a variety of practices that you can use to help manage fire blight. To obtain optimal control of the disease, an integrated pest management approach must be used, taking each of the factors described into consideration.

Blossom Blight

Figure 1: Blossom blight symptoms on pear. Photo credit: British Columbia Ministry of Agriculture and Land.
Description of this image precedes.

Figure 2: Early shoot blight symptoms, note: 'Bacterial ooze'. Photo credit: EarthTramper Consulting Inc.
Description of this image precedes.

Shoot Blight

Figure 3: Shoot blight symptoms - 'Sheaperd's crook'. Photo credit: EarthTramper Consulting Inc.
Description of this image precedes.

Figure 4: Shoot blight symptom on pear. Photo credit: EarthTramper Consulting Inc.
Description of this image precedes.

Canker

Figure 5: Rootstock canker. Photo credit: EarthTramper Consulting Inc.
Description of this image precedes.

Figure 6: Canker (smooth) on branch. Photo credit: EarthTramper Consulting Inc.
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Figure 7: Canker (cracked) on branch. Photo credit: EarthTramper Consulting Inc.
Description of this image precedes.

Fruit Infections

Figure 8: Advanced blight symptoms on pear fruit. Photo credit: EarthTramper Consulting Inc.
Description of this image precedes.

Figure 9: Advanced blight symptoms on apple fruitlet. Photo credit: EarthTramper Consulting Inc.
Description of this image precedes.

Site Selection

Cultivar and Rootstock Selection

Vigour Management

Manual Manipulation of Fruit Load and Vegetative Growth

Chemical Thinning at Bloom

Reduction of Humidity in the Orchard Microclimate

Insect Integrated Pest Management

Dormant Pruning: Orchard Sanitation

Pruning out fire blight cankers during the dormant season will reduce the number and distribution of sources of primary inoculum, which can fuel the next blight epidemic. This is best accomplished by removing and burning all infected (cankered) limbs each winter. This process should be conducted before any normal dormant pruning occurs.

Pruning during the Growing Season

Pruning out infections during the growing season can be extremely effective at limiting the number and distribution of secondary canker and shoot infections as well as reducing the risks for serious damage following summer hail and wind storms. Recommendations for removing fire blighted wood from the orchard during the growing season vary. Some experts advise pruning infected wood as soon as symptoms are visible, while others advise leaving the blighted terminals to “wall off” themselves and then dormant prune.

Prediction Models

Registered products and their use

Be sure to carefully read the label of any product that you intend to us in your orchard.

Selected References

Fire Blight Susceptibility of North American Apple & Pear Cultivars and Rootstocks

Least
Susceptible
Moderately
Susceptible
Highly
Susceptible
Apple Enterprise [1]
Freedom [1]
Jonafree [2],[3]
Liberty [1],[2]
Macfree [2]
Northern Spy [2],[3]
Red Delicious [1],[2]
Redfree [2],[3]
Ambrosia [5]
Cameo [4]
Cortland [2]
Creston [4]
Empire [1]
Golden Delicious [1],[2],[3]
GoldRush [1]
Golden Supreme [5]
Granny Smith [2]
Gravenstein [2]
Honeycrisp [5]
Jerseymac [2]
Macoun [2]
McIntosh [1],[2],[3]
Nova Easygro [1]
Nova Mac [5]
Pioneer Mac [4]
Sansa [4]
Spartan [1],[2]
Summerred [1]
Sunrise [4]
Yataka [4]
Braeburn [1],[3]
Fuji [1],[3]
Gala [1],[3] and Gala-types
Ginger Gold [1],[3]
Golden Russet [5]
Idared [1],[2]
Jonagold [1],[2]
Jonathan [2]
Lodi [2]
Mutsu [1],[2]
Paula Red [2],[3]
Pink Lady [5]
Rome Beauty [1]
Spigold [2]
Tydeman [2]
Wealthy [2]
Yellow Transparent [5]
Crabapple Dolgo [1] Manchurian [1]
Snowdrift [1]
Malus Rootstock B.9 [5]
M.7 [1]
Robusta [5]
Considered resistant:
Cornell-Geneva
(CG®) series [5]
MM.106 [1]
MM.111 [1]
M.4 [1]
M.9 [1]
M.26 [1]
M.27 [1]
Mark [1]
Ottawa 3 [1]
Pear Considered resistant:
Harrow Crisp [1]
Harrow Delight [1]
Harrow Gold [1]
Harrow Sweet [1]
Harvest Queen [1]
Kiefer [5]
Magness [5]
Moonglow[5]
Seckel [1]
Spartlett [5]
Anjou [1]
Bartlett [1]
Bosc [1]
Cascade [1]
Clapp’s Favorite [5]
Comice [5]
Flemish Beauty [1]
Starkrimson [1]
Asian Pear Kosui [1]
Chojoro [1]
Seuri [1]
Shinko [1]
Shinsui [1]
Singo [1]
Hosui [1]
Shinseiki [1]
20th Century [1]
Pyrus Rootstock Old Home (OH) [1]
OH x Farmingdale [1]
OHF 51 [1] Bartlett [1]
Quince [1]
[1] from OMAF and BC websites
[2] from MSU website, Nancy J. Butler, 'Diseases on Apples'
[3] from WV University, Kearneysville website, Keith Yoder and Alan Biggs
[4] from Drs. Steven Miller and Alan Biggs in NE183 plot, WV
[5] from other field observations and Cornell University data

This document was researched and assembled by Bernt Solymár of EarthTramper Consulting inc. and Tim MacDonald of Agriculture and Agri-Food Canada for the Canadian Horticultural Council. It has been reviewed and approved by experts in the field of integrated pest management. Funding for this publication was provided by the Pest Management Centre, Agriculture and Agri-Food Canada. Information on pesticides and pest control techniques are provided for information purposes only. Information contained in this publication is not intended to be used by growers as a production guide. Provincial publications should be consulted by growers for this information. Every effort has been made to ensure that the information in this publication is complete and accurate. Agriculture and Agri-Food Canada does not assume liability for errors, omissions, or representations, expressed or implied, contained in any written or oral communication associated with this publication. Errors brought to the attention of the authors will be corrected in subsequent updates.

Pesticide Risk Reduction Program Pest Management Centre

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