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Fire blight on fruit trees

POSTED: May 23, 2012 4:00 a.m.

Backyard apple trees are popular in this area of Georgia.

Many people see the apples being grown just down the road in Ellijay and assume it should be easy to grow them at home. While home fruit trees can be rewarding, they also require a lot of work. One reason for this is the prevalence of diseases.

Many folks have been reporting that their apple trees have been suffering from dieback at the top of a few branches.

This is a disease called fire blight. It is caused by bacteria (Erwinia amylovora) that live in sunken black cankers on the tree branches during the winter.

Fire blight can be identified by tip dieback several inches from the end of a branch and dark, black dead leaves. Dead leaves will also droop down in a distinctive ‘shepherd's crook.'

Sunken cankers may also be observed on the branches.

Fire blight affects many species of plants, including apple, crabapple, pear, cotoneaster, plum, cherry, flowering quince, hawthorn, pyracantha, serviceberry, roses, spirea and others.

After overwintering in the sunken cankers, the bacteria oozes out in the spring. This attracts bees and insects that help spread it around. It also spreads through the plant tissues and by means of rain, wind and pruning tools. Unfortunately, most people don't notice fire blight symptoms until now.

Any chemical control needs to be done in the early spring when new green growth is starting. The best control for fire blight now is to prune back blighted braches 12 inches below the signs of damage.

Between each cut, make sure to dip your tools in 70 percent isopropyl alcohol (rubbing alcohol) or a 10 percent Clorox solution (1 part bleach to nine parts water).

Avoid heavy nitrogen fertilization, especially in summer, because new succulent growth is very susceptible to fire blight infection.

UGA Plant Pathologist Elizabeth Little suggests the best method of control for fire blight is to plant resistant fruit tree varieties.

Apple varieties such as ‘Gala,' ‘Pink Lady' and ‘Fuji' are highly susceptible and should not be planted.

Varieties with some resistance are ‘Suncrisp,' ‘Gold Rush,' ‘Arkansas Black,' and ‘Cameo.'

Pear varieties like "Bartlett' and ‘Comice' are not resistant and should be avoided.

"Moonglow,' ‘Maxine,' ‘Seckel,' and ‘Kieffer' are pear varieties that can be grown in our area. When using resistant varieties, Fire Blight may still infect the trees.

However, most infections will not be severe enough to kill the tree and can be managed by proper pruning.

Chemical control can be used for fire blight management.

Sprays of copper hydroxide and streptomycin can be applied to infected trees during spring greening and at bloom.

However, it can be difficult for most homeowners to get the proper spray coverage necessary to control the infection.

Also, if used too often, the bacteria may develop resistance to the chemicals.

Copper applications can also be phytotoxic, which means they can injure the plants. These sprays must be made at the right time of tree development and during the right temperature conditions. Contact the extension office for suggestions on spray times and use rates if you are considering chemical control.

Clark MacAllister is the Dawson County extension agent. For more information, call (706) 265-2442.

 

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