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Early spring also brings early problems

Posted: April 14, 2012 - 11:11pm

The mild winter and early spring did more than make flowering plants bloom early. Some disease problems are showing up a little early as well.

One of these is fire blight on pear trees. Fairy ring is showing up in lawns, and I have seen winter-kill on centipede.

Fire blight is a destructive, highly infectious and widespread disease caused by the bacterium Erwinia amylovora. It attacks blossoms, leaves, shoots, branches, fruits and roots.

The pear trees I have seen have ends of limbs dying, turning brown and then black. Fire blight is more severe when the weather is warm and wet, and when the pear trees are blooming. This year, the conditions were perfect for fire blight.

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.

Pear trees infected with fire blight need to have the infected limbs removed. The proper way to prune out the infected parts is to follow the infection down the limb to the first green leaf, then cut the limb off 8 to 10 inches past that leaf.

After making the pruning cut, the pruners should be disinfected. The best way to disinfect is with 70 percent rubbing alcohol or a 10-percent chlorine solution. A 10-percent chlorine solution can be made by mixing one part bleach with nine parts water. If the pruners are not disinfected, the disease can be spread each time a new cut is made.

When the pruning job is finished, the pruners should be cleaned and oiled to prevent the chlorine solution from damaging the pruners.

Fairy ring is a disease of lawns that is caused by approximately 40 different fungi. This problem usually occurs in late spring through the fall, but this year it is early because of the warm weather and low rainfall.

I have fairy ring in my yard. Fairy ring symptoms vary with the fungi that are causing the problem. Typically, this disease has outer rings that are either dark-green or brown. The shape and size of the rings vary depending on the species. The fungi that cause the grass to be dark green are producing nitrogen as a byproduct, while the areas that turn brown are caused by the fungi producing arsenic.

In some cases, there will mushrooms in the affected area. The fungi responsible for fairy rings are breaking down organic matter in the soil.

Most of the control options deal with how the grass is managed. First, proper irrigation is important. These byproducts of the fairy ring can be leached out of the soil by watering these areas heavier than the rest of the lawn. Also, aerate and dethatch the lawn to allow the water to penetrate the soil more easily and to remove thatch that has built up.

The last option is to use a fungicide to control the disease. There are few fungicides that will work on fairy rings and they are expensive. Flutalonyl (Prostar) or azoxystrobin (Heritage) can help to control it.

With the mild winter, I was not expecting to see much winter-kill in centipede, but I have seen a few lawns where this has occurred. .

Winter-kill is caused by a combination of factors. The first is mowing height. Centipede should be mowed at 1½ inches high.

This measurement is taken from the soil surface. When centipede is mowed at 2 inches, the stolons of the centipede are unable to root down into the soil. This keeps the roots in the air and the cold weather kills the stolons.

Other reasons for winter-kill are too much nitrogen fertilizer and improper irrigation. Thatch buildup and shallow watering cause a shallow root system.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net, or at (706) 836-2152.

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