Sap ooze from fireblight on apple Canadian Forest Service	Characteristic "Shepherd's Crook" Ohio State University Extension Service

Introduction

Fire blight is the enemy of rosebushes and apple and pear trees.  It is caused by a bacteria (Erwinia amylovora) which attacks starting generally from the blossoms or flowers and moving up to the twigs and then the branches.  Fire blight gets its name from the burnt appearance of affected blossoms and twigs.  Flowers turn brown and wilt; twigs shrivel and blacken, the ends often curling.  In more advanced cases of bacterial infestation, cankers, discoloured oozing patches, form on branches.  The translucent amber or reddish ooze (see top left image) contains masses of bacteria. Heavy persistent infections can be fatal.

Which Plants are Affected?

Most common rose varieties are vulnerable to fire blight infection.  Many varieties of pear and apple trees (see image) are also susceptible although some varieties are more at risk than others.  Other susceptible trees include mountain ash, hawthorn and cotoneaster.  Check with your local nursery or garden centre for information on specific species before you purchase if fire blight is a concern.

How does it Spread?

Fire blight bacteria is easily spread by many means: rain splashes carrying bacteria from one plant to another; birds, insects or animals; an infected plant rubbing against its neighbour.  Even gardeners can unwittingly transmit the bacteria on infected gardening tools or when watering.   The time of maximum risk of infection is late spring or early summer when the bacteria emerge from their dormant period and the oozing from cankers is most pronounced.

How do I Control Fire Blight?

There is, as yet, no cure for fire blight and the best way to deal with the infection is to remove infected stems and branches cutting no less than 8 inches up from the infected area.  Because the bacteria are so easily transmitted, care should be taken in disposing of infected plant material. Either burn or discard in the trash.  Do not leave infected material where the bacteria might be spread to surrounding bushes or trees.  Care should also be taken with tools which have come into contact with the bacteria.  Tools can be sterilized in an alcohol solution (three parts denatured alcohol to one part water).  Diluted household bleach can also be used (one part bleach to nine parts water) as long as the tools are wiped dry after disinfecting to prevent corrosion.

A variety of bactericides have been developed to combat fire blight, many of the most common containing streptomycin sulphate.  Check with your local garden or landscape centre for details and remember to follow the instructions carefully.

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