Recent wet, cool weather facilitates perfect conditions for plant diseases

There are two diseases that occur more often during cool, wet conditions, like we have had this spring. They are fire blight in apple and pear trees and leaf gall in azaleas and camellias.

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How do you know if you have fire blight in your plants? When you look at a fire blight-infected tree from a distance, you can see the dead tips of the limbs. We call this flagging.

Also, the branches at the end of the limb might be bent in the shape of a shepherds 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.

So, how does fire blight infect our plants? Fire blight enters the plant through natural openings, such as flowers. It also enters through cracks in the bark or other wounds. Fire blight attacks new growth on the plant and then spreads to older growth.

Fire blight 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 that the plants start to flower.

If your trees are infected with fire blight, remove the infected limbs. The proper way to prune out the infected parts is to follow the infection down the limb until you come to the first green leaf on that limb. Cut the limb off eight to 10 inches behind the first green leaf.

Disinfect your pruners after every cut with a solution of 70 percent rubbing alcohol or 10 percent chlorine mixed with water. If you don't disinfect your pruners, you will spread the disease each time you make a new cut. After you finish pruning, clean and oil your pruners; the chlorine solution can damage them.

If your plants are infected by fire blight, start pruning as soon as you see the disease. Watch the plant closely and remove infected branches as they appear. Then, next spring, spray the trees that were infected with the antibiotic Agrimycin.

Agrimycin can be hard to find. If you can find it, spray the trees during the bloom stage. Spray starting at bloom and repeat every three to four days while the tree is blooming.

You also can use a copper fungicide, such as Kocide. Spray with a copper fungicide 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.

Another way to reduce the chance of fire blight is to plant resistant varieties. There are a number of resistant varieties on the market and it pays to ask if the variety of apple or pear you are planting is resistant.

Another disease to watch out for is leaf gall.

If the leaves on your azaleas and camellias appear light yellow, puffy and will crack open, this is leaf gall. In camellias, only the underside of the leaf will be off-colored. The top part of the leaf will be the same color.

As the gall ages, it turns white. When it does, it is releasing the spores that will infect the plant the next spring. After the spores are released, the leaf turns black and falls off the plant. The spores will infect the plant next year when the leaves and buds begin to open.

Since there is such a small window for treatment, it is not recommended that fungicides be used. Once the buds are open, it is too late to control the disease. So, what needs to be done to help control it?

The first thing is sanitation. When you first see the leaves, remove them from the plant before they turn white and start releasing the spores. When you remove the diseased leaves, put them in a plastic bag and get rid of them. Remove any mulch, and replace it with fresh mulch. This will help remove some of the spores.

Leaf galls do not cause much damage to azaleas and camellias, and the plant can survive. However, fire blight can weaken trees. It usually takes a number of years to weaken a tree to the point where it can't recover, so it is best to work on fire blight-infected trees as soon as you see the disease.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/columbia.