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Fireblight attacks trees, shrubs, causing limbs to blacken, die

Posted: Sunday, May 09, 2010

I recently saw a problem on some pear trees that I didn't think we would see much of this year. The ends of the trees' limbs were dead, turning brown and then black.

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The problem is a bacterial disease called fireblight, a destructive, highly infectious and widespread disease caused by the bacterium Erwinia amylovora . Fireblight attacks blossoms, leaves, shoots, branches, fruits and roots.

I didn't expect to see much of this disease this year because of the dry conditions. Warm, wet conditions are necessary for the bacteria that causes fireblight to spread.

Not all plants are affected by fireblight, only those in the family Rosaceae. These plants include trees and shrubs, such as flowering quince, cotoneaster, hawthorn, loquat, apple, crabapple, photinia, flowering plums, cherries, pyracantha, pear, rose and spirea. The plants that I see fireblight on most are apple, crabapple and pear.

Signs of fireblight in plants include leaves at the end of limbs turning black or deep rust colored. The dead tips of the limbs are visible from a distance. This is called flagging.

Also, the branches at the end of the limb may be bent in the shape of a shepherd's crook. The bark at the base of the blighted leaves becomes water soaked. These areas then turn dark, appear sunken and dry. Cracks can develop at the edge of the sunken area.

Fireblight enters the plant through natural openings such as flowers. It also enters through cracks in the bark or other wounds. Fireblight attacks new growth on the plant and then spreads to older growth.

Fireblight can be spread from infected plants to healthy plants by rain, wind, insects and humans. The bacterium spends the winter in sunken cankers on infected branches. When the weather warms, the bacterium oozes out of the cankers. Bees and other insects are attracted to the bacterium, and they spread the disease to other plants. The bacterium starts to ooze about the same time the plants start to flower.

The best option for control is to plant varieties that are resistant to fireblight. The original Bradford pear trees are resistant to fireblight. However, Bradford pears have been replaced by other varieties of pears because of the problem with Bradford pears splitting or breaking apart. Most of the newer varieties of pears are not resistant to fireblight, but they are not subject to breaking apart.

The second option for preventive control is to spray the trees during bloom with the antibiotic Agrimycin, which can be hard to find. It needs to be sprayed on the trees during the bloom stage, starting at bloom and repeating every three to four days while the tree is blooming. A copper fungicide, such as Kocide, also can be sprayed every seven days during the bloom. With either of these products, repeat the application if it rains. Also, make sure to follow the directions on the label.

The infected limbs of trees infected with fireblight should be removed. The proper way to prune out the infected parts is to follow the infection down the limb to the first green leaf on that limb, then cut the limb off 8 to 10 inches past that green leaf. After making the pruning cut, disinfect the pruners with solution of 70 percent rubbing alcohol or a 10-percent chlorine solution made by mixing one part bleach with nine parts water.

Failing to disinfect the pruners can spread the disease each time a new cut is made. After pruning, clean and oil the pruners; otherwise, the chlorine solution can damage them.

Plants infected by fireblight should be pruned as soon as the disease appears. Watch the plant closely and remove infected branches as they appear. Then, next spring, spray the trees that were infected.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net.

Russell Rainey displays some of the soaker hoses at the Ace Hardware store in Evans. Rain barrels and soaker hoses are effective ways to conserve water.



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