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James A. Chatfield, Ohio State University Extension, Northeast District/Horticulture and Crop Science; Nancy A. Taylor, Erik A. Draper, Stephen Nameth, Joseph F. Boggs, |
Callery Pear
This bacterial disease (Erwinia amylovora) was unusually severe on Callery pears in areas of Kentucky, southern Indiana, and southern Ohio and to a lesser extent further north in 2001, presumably due to warm, wet weather events that occurred during bloom. This is because such conditions, especially temperatures above 60F, are known to encourage blossom infections. The number and severity of infections surprised many, especially since early spring conditions seemed generally dry. The spotty occurrence of the outbreaks may relate to localized showers during peak bloom times.
Symptoms include numerous infections (in some cases dozens or hundreds) along the stems where blossom clusters developed. Affected plant tissue is browned and blackened with discolored leaves remaining on the tree and shoots often wilted in a "Shepherd's crook"-like fashion. In most years, fireblight on Callery pears is far less severe in terms of the number and extent of infection than fireblight on some of the more susceptible fruiting pear and apple cultivars.
One of the typical control recommendations for fireblight has always been to prune infected shoots 6" or 8" below the infected area to limit the spread of the disease. However, there is a little more to this disease than meets the eye, or pruners. John Hartman, Extension Plant Pathology with the University of Kentucky, wrote an extensive article on fireblight in the June 2001 issue of Kentucky Fruit Facts (http://www.ca.uky.edu/HLA/fruifact/).
Hartman wrote that growers and gardeners with fireblight infected trees are often tempted to remove infected branches. In many cases, this would be the wrong strategy, because removing branches can encourage new shoots to develop, and these new shoots would also be susceptible to new infections. If fireblight strikes are discovered early, before leaves have turned completely brown, timely removal of infected shoots can help slow the spread of the disease. However, most growers and gardeners do not discover the disease early enough for this to be helpful.
For most growers, Hartman recommended letting the disease run its course, allowing the tree defense to stop fireblight spread within the tree. Dead shoots and branches should be removed in winter when there is little chance of spreading this disease.
Crabapple
In the National Crabapple Evaluation Program plots at Secrest Arboretum on the Wooster campus of the Ohio State University's Ohio Agricultural Research and Development Center, the incidence of fireblight is typically minor in most years. However, 2001 turned out to be a banner year for fireblight on crabapple, much worse than any in the past 10 years.
Young plants of several crabapple cultivars developed severe fireblight strikes that blighted nearly half of the foliage and stem tissue. These heavily affected cultivars included 'Golden Raindrops,' 'Sinai Fire,' 'Foxfire,' and 'Silver Moon.' Nevertheless, most of the cultivars in the plot that exhibited fireblight this year had only a minor incidence, and the majority of cultivars in the plot had no fireblight.
It will be intriguing to follow the incidence of fireblight in the trees that were badly damaged this year to see if the problem worsens in coming years.