Many folks are successfully growing a few fruit trees in the back yard. This is a great idea. Hopefully, your planting, fertilization and pruning have been successful.

However, there is one problem that you should know about because it can kill your trees in one season if not kept under control. That is FIRE BLIGHT. Fire blight is a bacterial disease caused by Erwinia amylovora that can severely damage and even kill apple and pear trees. Blossoms, fruits, fruit spurs, twigs and branches are affected, and sometimes the entire tree may be killed.

A brown blight on the tips of a few branches is usually the first symptom observed in the spring. Blighted twigs and watersprouts wilt at their tips, giving the appearance of a shepherd's crook. Fruit blight generally occurs in immature fruits. The fruit first appears oily or water-soaked; often droplets of milky-like ooze form on the surface. The fruit shrivels and remains attached to the branch.

The bacteria can move in the vascular system of the tree, and this dieback of infected twigs can lead to death of larger branches or the trunk. During humid or rainy weather, blighted tissues usually exude a milky-like, sticky liquid or ooze containing the bacteria. The appearance of blighted tips of branches and ooze on the surface of fruit or twigs or would is a very distinctive diagnostic characteristic of fire blight.

The bacteria overwinter in diseased and dead tissue (cankers) on a tree or shrub. In this area, I see infections on numerous Bradford ornamental pear trees. These ornamental pears are not killed by Erwinia amylovora but serve as a reservoir for the bacteria. This bacteria has been reported to also infect photinia, cottoneaster, Indian hawthorn, flowering crabapples and pyracantha.

In the spring, bacteria are carried by wind, rain and insects to blossoms or growing, succulent shoots. Bacteria can enter through natural openings in the flower or through stomata in the leaves. However, wounds and injuries made by insects, hail, wind or by pruning are important means of entrance. From these primary infections, the bacteria may be carried to other blossoms, twigs or fruits resulting in secondary infections.

Removal of Infection Sources -- Removal of all cankers and blighted twigs is very important. The trees must be monitored and new infections must be promptly removed as soon as symptoms are seen. Cuts should be made 10-12 inches below the area where the blight occurs. Care must be taken to prevent spread of the bacteria by hands or cutting tools. If infections are cut out, use bleach (Clorox), dilute 1:10 with water to sterilize the cutting tools between each cut. All wood pruned from an infected tree should be destroyed and apply oil to the pruners so they don't rust.

Chemical control is an option for folks with an orchard of significant size. Agricultural streptomycin (Agrimycin, Agri-Strep) in sprays 1 teaspoon/gal) applied at five-day intervals beginning when 5-10 percent of the blossoms are open and continuing until petal fall with 2-3 sprays after petal fall at 7-10 day intervals will reduce the occurrence of fire blight. Streptomycin should not be applied closer than 50 days to harvest on apples and 30 days on pears. Streptomycin is an approved organic product.

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Call the Master Gardener here in Orange County for information about gardening at (919) 245-2061. They are in the office at 306 Revere Road, Hillsborough, from 10 a.m. to noon Monday through Friday.

Carl A. Matyac is a N.C. Cooperative Extension agent of horticulture at the Orange County Center on Revere Road in Hillsborough. Call (919) 245-2062 or e-mail carl_matyac@ncsu.edu