Fire Blight on Apple & Pear Trees

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Q:  Why are the tips of branches turning black on my apple and pear trees?

 A:        We have seen many questions over the past couple of weeks where the leaves on branches of apples and pears turn black or brown at the tips. This usually refers to a disease called fire blight. Fire blight is a disease that can appears quickly on apple and pear trees during in the spring into early summer. This disease can severely damage infected trees and sometimes may kill the entire tree. Fire blight develops more rapidly when temperatures are 65 to 90°F combined with humid or rainy weather. Once the disease is established, it can be very difficult to control.

Fire blight is a bacterial disease that can infect the blossoms, fruits, twigs, and branches. The very first symptom of the disease starts in the spring with the fruit tree blossoms. The blossoms will appear water-soaked, wilted, shriveled, and finally turn brown to black.

The twigs and branches will soon begin to wilt at the tips giving the appearance of a shepherd’s crook. As with the blossoms, the twigs and branches will finally turn brown to black. As the twigs and branches turn brown so will the leaves. The infected leaves will remain on the branches giving the appearance that a fire went through the tree, hence why the disease is called fire blight.

The bacteria within the plant will continue moving down the branches and twigs causing them to turn brown downward from the tips. Immature fruits on the infected branches will turn brown and will eventually shrivel up while remaining on the branches. During humid or rainy weather, a sticky liquid or ooze could be found on the surface of infected plant parts. This ooze is a very distinct characteristic of fire blight.

So where does this disease come from? The bacterium that causes fire blight overwinters in diseased and dead tissue on the tree. In the spring, the disease is carried by wind, rain, and insects to blossoms or new shoot growth on apple and pear trees. The bacterium enters through natural openings in the flowers and leaves along with wounds and injuries made by insects and pruning.

When it comes to controlling fire blight on apple and pear trees, unfortunately it is a difficult disease to control. However, there are some control practices that can help reduce the severity of fire blight.

The best way to reduce the chances of fire blight is to purchase varieties of apple and pear trees that have some resistance to the disease. There is not a variety that is completely resistant to fire blight, but there are varieties that vary in resistance and will be helpful in reducing infection. In North Carolina, the more susceptible apple varieties include Jonathan, Golden Delicious, Lodi, Yellow Transparent, Stayman, and Gala. Red Delicious is generally less susceptible to fire blight. Pear varieties that are highly susceptible include: Bartlett, Bosc, and Clapp’s Favorite. Kieffer, Orient, Starks Delicious, and Dawn are pear varieties that are less susceptible to fire blight, while Magness and Moonglow are relatively resistant.

Sanitation practices are some of the best ways to managing fire blight by removing all infected branches and twigs before growth starts in the spring. Cuts should be made 4 to 6 inches below any evidence of dead tissue. Pruning newly infected twigs and shoots reduces spread of the disease if done carefully. Apple and pear trees should be monitored daily and new infections must be promptly removed as soon as symptoms are seen. Cuts should be made 10 to 12 inches beyond the last evidence of the disease. Great care must be taken to prevent the spread of the bacteria by hands or cutting tools. When infected branches are cut out, use a 10% bleach solution to sterilize the cutting tools between each and every cut.

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Jessica Strickland is an Agriculture Extension Agent, specializing in horticulture for North Carolina Cooperative Extension in Wayne County. Horticulture program information can be found at //wayne.ces.ncsu.edu/. Forward any questions you would like answered from this week’s column to Jessica.Strickland@waynegov.com.