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Fireblight
Mary Small
Extension
Agent, UIP
Jefferson,
County
"Does my plant have fireblight?" is an
often-asked question each year. Based on weather conditions, Clinic samples and
observations, fireblight is appearing in many areas along the Front Range.
Branch bent over in a
"shepherd's crook"
Click on image to enlarge
Fireblight may first appear as "blossom
blight". Flowers turn brown, shrivel and remain attached to the plant.
Affected leaves also turn brown to black, wilt and remain attached. Branch tips
bend over in a "shepherd’s crook." Cankers (dark, sunken areas) are
present on stems, branches or trunks. Conductive tissue under these cankers is
killed, reducing or cutting off water movement in the affected areas.
Creamy-colored, gooey bacterial ooze droplets are found in and around the
canker.
Gooey bacterial ooze
Click on image to englarge
Plants affected by fireblight include those in
the rose family that form a pome-type (apple-like) fruit. Examples are mountain
ash, apple, crabapple and pear. Even "disease-resistant" varieties of
these plants can be infected. "Resistant" does not mean
"immune". Stone fruits like peach, cherry and plum do not get
fireblight.
Crabapple tree with fireblight
Click on image to enlarge
Many other problems are mistaken for fireblight.
Transplant shock, freeze injury, fungal diseases and root injury from compacted
soil, drought and excess soil moisture all mimic the disease.
After diagnosis, the best way to manage
fireblight is to prune out affected tissue. During the growing season, locate
the base of the damage on the affected twig or branch. Move to a point that is
6-12 inches below that and make a pruning cut. Disinfest the pruning tool
between each cut, using rubbing alcohol, a disinfestant spray or a mixture of 1
part bleach in 9 parts water. This helps prevent the spread of the fireblight
bacteria that may be on the pruning tool. During the dormant period, the tool
does not have to be disinfested. Clean the pruners thoroughly when the job’s
done to prevent corrosion. Preventive copper sprays may be applied during the
dormant period only. Sprays alone will not control fireblight.
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