Fungus blight on pear trees is known as "fire blight." Among the problems pear trees can have, fire blight is one of the more serious. But this fungal disease can be controlled by pruning and applying a bactericide. Fire blight resistant pear trees have been developed, but the fruit produced by these partially resistant trees is of poorer quality.
The bacteria that causes fire blight is Erwinia amylovora, which first attacks the blossoms, then moves to the twigs and finally attacks the branches. The symptoms are brown and wilted flowers and shriveled/blackened twigs. It is called fire blight because of the burnt appearance. In severe or advanced cases of this blight, the branches develop cankers or patches that ooze a reddish liquid. These oozing cankers are filled with masses of the Erwinia amylovora bacteria. A pear tree that has a severe and persistent fungal infection can die.
How It Spreads
There are several ways the bacteria is spread: splashing rain distributes it, and birds, insects and animals can transmit the disease. Gardeners also unknowingly transmit the disease when they prune an infected branch and fail to clean their pruning shears, or when they water the pear tree--the water distributes the fungal bacteria from one location to others. Late spring or early summer is the time the bacteria ends its dormancy period, making late spring or early summer the time of greatest risk for fire blight. Canker oozing is at its optimum during this time.
Control of Fire Blight
There is no known cure for fire blight; the only way to control the disease is through pruning of infected branches and use of a bactericide. When pruning, make sure you have cut off the entire area of infection, cut off approximately 8 inches or more in advance of the infected area. The infected material should be destroyed through burning or the trash. It should never be put in a compost bin or left to lie out in the garden--it can easily be spread to other trees. Pruning shears should be sterilized after cutting away the infected material by dipping the pruning blades in alcohol or bleach and then wiping them dry. There are several bactericides that can be used to fight the disease; many contain streptomycin sulphate.
Plants That are Affected
The pear tree is just one of the many plants that can be affected by fire blight, although there are some species that are more susceptible than others. Some species of apple trees can be infected. Deciduous trees such as the mountain ash, hawthorn and cotoneaster can also be affected.
Fire Blight Resistant Pear Trees
According to the Yardener, fire blight resistant pear tree varieties include: Asian varieties and Comice, Dawn, Douglas, Duchess d'Angouleme, El Dorado, Fan-Stil, Harvest Queen, Lincoln, Luscious, Mac, Magness, Maxine, Moonglow, Oriet, Seckel, Starking Delicious, Sugar, Sure Crop, Waite and Winter Nelis.