Managing fire blight on ornamentals
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Several landscape professionals are reporting damage caused by fire blight. Fire blight is caused by Erwinia amylovora, a bacterial pathogen. The disease is best known for the severe damage it causes in fruit orchards, but several common landscape plants are also susceptible. Cotoneaster, flowering crabapple, flowering pear, hawthorn, photinia, pyracantha and mountain ash are all susceptible.
Blossoms are particularly susceptible to infection; infections initiated
in the blossoms can move into the woody tissue, causing shoot damage.
Disease is commonly spread by insects and splashing rain or irrigation.
Infected plants have a scorched appearance with young shoots wilting and
turning brown. The shepherd-crook shaped dead tips are a good
diagnostic symptom of this disease. Samples of live, symptomatic tissue
can be submitted to MSU’s Diagnostic Services for confirmation. Diagnosis can be performed with a molecular based test (PCR), which is very sensitive.
The disease is favored by excessive nitrogen fertilizing and heavy
pruning, which both lead to more succulent growth. Tolerant or resistant
cultivars of some the above mentioned plants are available. Results of
studies on resistant species across the United States are inconsistent,
therefore, nursery growers need to do some cultivar evaluations to
determine the best ones for their area.
To manage this disease sanitation is the best strategy. If your nursery
is located near old pear, apple or quince trees, these abandoned trees
can be a reservoir for the inoculum. You should consider removing them.
Where low levels of infection occur, the infected tissue should be
pruned out, make pruning cuts several inches below the edge of the
infected area. If pruning is not possible, affected plants should be
removed from the nursery and destroyed. Sterilize pruning tools or
shears between cuts with either 10 percent household bleach or 70
percent alcohol.
Copper-based bactericides like Phyton or Kocide may be helpful. These
materials limit the amount of bacteria on the plant surface, but should
not be relied upon as the sole management strategy. Efficacy of
applications can be maximized by using predictive models. The commercial
fruit industry uses predictive models that are based on recent
environmental factors, and the biology of the pathogen to optimize the
timing of chemical applications. One such predictive model (derived from
the Maryblyt model) is available online at MSU’s Enviro-weather
site. Users must regularly monitor the predictive results during bloom
time, but landscape managers looking for a more inclusive management
program may benefit from the information provided by the model.
Additional information about fire blight is available on the MSU IPM web
site at: http://www.ipm.msu.edu/fruitpests/fireblight.htm
