Managing fire blight on ornamentals

Editor’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

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