Fire Blight - This is caused by the bacterium Erwinia amylovora and affects common fruit trees such as Apple and Pear trees. Of Pear trees, Pyrus kawakamii is the most susceptible while Pyrus calleryana is very resistant showing almost no symptoms in most cases. The disease enters the tree at the time of blossom through meristems and flowers forming lesions on the young branches and leaves. Branches die at the meristems at first and move back leaving dead leaves attached to the tree.
If left untreated, the disease can kill shoots, leaves, limbs, blossoms and occasionally the entire tree.
Fire Blight overwinters on infected bark and is spread by splashing rain, dew, wind and insects. It
spreads rapidly during moist humid weather, especially during time of bloom. Other trees and plants
which are commonly infected include, Cotoneaster, Fruiting Pear, Pyracanth and roses.
When planting use resistant varieties. Avoid heavy pruning or excess nitrogen applications which
stimulate new succulent growth and can be easily infected. Sanitation is important and fallen leaves
should be removed as they harbor disease. Trim in hot summer months when spores are latent. Trim
to remove dead wood and infected branches where possible. To prevent spread of disease, clean
trimming tools using 10% alcohol or 20% chlorine bleach and 80% water. Annual treatment of the
disease will offer suppression – not a cure. Treatment should be applied as a foliar spray using
Streptomycin sulfate as the active ingredient in fall prior to leaf drop and twice in spring at bloom 7
days apart. For optimum results more than two applications may be required in spring every 5 to 7
days during bloom time.