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Extended drought is hurting trees

Posted: May 12, 2012 - 11:15pm

I have been getting numerous calls about trees that have dead limbs near the top, or trees producing fewer blooms or leaves than in years past.

Large trees have plenty of reserves stored so they can still flower and leaf out for a number of years before drought, root damage or something else causes the tree to suffer. The drought of the past two years has caused a number of our trees to use up their stored energy, and they are in a state of decline. When the tree starts declining, the area of the tree the greatest distance from the roots will be hit hardest, which is why the limbs in the top of the tree are dying.

Also, stressed trees are more prone to insect and disease problems than healthy trees. I am seeing oak, maple and elm trees with dying limbs.

This is not a problem with the roots. This is a widespread insect problem called scale. Infested branches will have brownish, red bumps on the limbs. These are the scale insects.

Once they start feeding, they are immovable. They will spend the rest of their lives at that spot. In the spring, their eggs hatch and the young move to find a spot to start feeding. This is called the crawler stage and is the easiest time to control them.

There is a systemic insecticide called dinotefuran that can be used to control this insect. Homeowners can find this in a product made by Green Light called Safari. When applied around the root system, the insecticide moves through the plant and kills the scale as they feed.

Another way to help reduce the problem is to remove the limbs that have the scale on them. This will work if there are a few infested limbs, but if numerous limbs have scale on them, it could do more harm to the tree to remove the limbs.

To help trees recover from the drought, mulch should be placed around them. Mulches help the trees recover by conserving soil moisture and reducing soil erosion and water run-off. Mulches can reduce the summer soil temperature, which creates a better environment for the root system. Large mulched areas also protect the tree from lawn mowers and weed eaters.

The mulch needs to be 3 to 4 inches deep, and extend to the edge of the canopy or farther. As the tree gets larger, increase the size of the mulched area to encompass more of the root system. Don’t put the mulch up the trunk of the trees. This encourages the root system to grow into the mulch. It can increase the chance of diseases and insects attacking the trunk of the tree, and it reduces the growth of the tree.

The next practice that can help trees recover is to lightly fertilize them. Use a complete fertilizer, because phosphorus aids in root development. Phosphorus is the middle number on the fertilizer bag. If there is grass or shrubs under the tree, the amount of fertilizer that is used on these plants will help the tree and it doesn’t need additional fertilizer.

Pine trees also are dying all over the county. Some of these trees, especially smaller ones, are dying from the drought, but most of the trees are being attacked by pine beetles. There are three pine beetles that attack pines: the black turpentine beetle, IPS engraver beetle, and the Southern pine beetle. The IPS engraver beetle and the Southern pine beetle are more prevalent. The majority of the beetles have left the tree by the time the needles on the tree turn brown.

The best control option for these beetles is to cut the tree down at the first symptoms of the tree being killed by the beetles. By laying the tree on the ground, the beetles are confused when they emerge from the tree. Then the tree needs to be removed from the property. There is an insecticide that contains bifenthrin that will help protect the trees, but it needs to be applied to the whole length of the tree.

Trees can recover from the effects of the drought if we help them out by controlling insects, mulching, and giving them extra water.

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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