Monday, June 8, 2009

Landscape - Fire Blight

Fire blight is being seen in ornamental pears and other landscape plants at this time in Delaware. The following is a good article on the subject from Rutgers University.

Fire blight is a relatively common disease caused by a bacterium (Erwinia amylovora). Fire blight can occur on many rosaceous plants, including crabapple, cotoneaster, hawthorn, mountain ash, pyracantha, and pear. Although we see this disease most often in pyracantha, some ornamental pears in central New Jersey have been recently diagnosed with the disease. Development of fireblight usually begins in the spring as bacterial cells ooze in a yellow-amber liquid from existing cankers on infected plants. These cells are spread to susceptible flowers, leaves, fruit, and stems by insects, wind, splashing rain, or pruning equipment. Insects are especially attracted to this sweet, sticky, bacterial ooze; bees and other pollinating insects commonly pick up bacteria while visiting the cankers and subsequently deposit the cells on developing flowers. Erwinia bacteria penetrate tissue through wounds and natural openings such as stomates and nectaries. Twigs and branches infected with the pathogen die rapidly and appear scorched, hence the name “fireblight.” Tender shoots tend to droop and bend as they die, developing a symptom commonly associated with the disease called a shepherd’s crook. As the disease advances, cankers form at the base of infected branches, and highly susceptible plants may die. Conditions optimal for fireblight development are extended periods of warm (greater than 65 to 75 F), wet weather during spring.

To manage the disease, improve plant vigor, but avoid heavy spring fertilization that would promote succulent growth. In late summer (after bacterial oozing no longer occurs), prune all diseased wood at least 6 to 8 inches below the infection, surface sterilizing tools between cuts. Remove water sprouts, and dispose of any infected plant material which may harbor the pathogen. The following bactericides have labels for fire blight (check for host, timing, and rates): copper (Badge, hydroxide, metallic, salts, sulfate), fosetyl- Al (pre-bloom and repeat every 7 days until bloom), Junction (5-day intervals during bloom), OR phosphite (7-day intervals through bloom). Finally, consider repeatedly diseased, highly susceptible plants with material that is more resistant to this disease. Highly susceptible callery pears include Aristocrat, Autumn Blaze, Capital, Fauriei, and Redspire; moderately susceptible cultivars include Cleveland Select, Earlyred, and Whitehouse. Although Bradford is reported to be moderately resistant in certain locations, it will develop fireblight under conditions optimal for disease development, as we noticed last year.

Fire blight on ornamental pear. Photo from the Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services,

Information from Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers University.

No comments: