San Antonio Express News
GARDENING, Etc.
Sunday, August 8, 2004
by Lynn Rawe
Trees have been an intricate part of landscapes for centuries. Trees have always been valued, whether as a means for shading the house and yard, or an aesthetic part of the landscape.
Today people still value trees, and homeowners want to protect these valuable assets. When trees begin to have problems, you look for answers. Some problems are treatable while others are not. We will discuss some problems and identify their possible causes.
The earlier rains this spring and summer were wonderful for the aquifer, but have caused many fungi to appear on our plants. Trees have been hit especially hard. Fungal leaf spots have appeared on many types of trees. Moisture on the leaf surface and high humidity is the primary cause of fungal leaf spot. Rake and dispose of diseased leaves to prevent spores from spreading. It may be necessary to spray the trees with a registered fungicide like Fung Away or Immunox. If you don’t have a way to spray the top of the trees, you may need to hire a reputable tree service.
Another common problem that occurs with trees is root damage. Many things can contribute to root damage. If you see decline of limbs or dead leaves in the top of the tree, root damage is a possibility.
Changing the original soil level can slowly cause damage to trees that may take three to five years to appear. Either reducing or increasing the original soil level can result in root damage. Never add soil around the trunk of a tree. A safe amount of soil to add over tree roots annually is only about one inch.
Too much moisture can cause a water logged condition in soils, reducing oxygen to the roots. Excessive amounts of water for extended periods of time will cause the tree’s roots to rot. The water fills up the air space in the soil eliminating oxygen, and the tree basically drowns.
Healthy roots help to move water and nutrients up and down the tree. If the roots are damaged, water cannot circulate toward the top of the tree, causing defoliation and sometimes death to limbs.
Construction around trees can cause a variety of problems. Cars, trucks or big machinery can cause compaction of the soil. Compaction presses the soil particles together leaving the soil hard and without air space. Vehicles can bump and damage the bark, causing vascular damage to the tree. This type of abuse disrupts the tree’s ability to transport water and nutrients throughout. Decks, driveways or walkways may cover a portion of a tree’s root system. This hampers the natural movement of water reaching the root system, and results in slow, but constant damage to the tree.
Probably the number one cause of tree death is “weed eater” damage. Repetitive use of a “weed eater” around trees, knocking off bark, eventually causes girdling of the tree. Eliminate the need for “weed eaters” around trees by removing grass and weeds, and replace with mulch or groundcover.
Girdling can also be caused by anything wrapped around the trunk for an extended time. Wire is used on ball and burlapped trees to hold the roots intact. If the wire was forgotten and left, the girdling process will slowly kill the tree as the girth of that tree becomes larger. If young trees are stacked, the stacking should be removed no more than one year later.
Some young trees have thin bark. Red oaks and fruit trees fall into this category. Sun scald can occur of the southwest side of the tree, causing the bark to split. This can be prevented by either wrapping the tree with a tree wrap from your local nursery or leaving low branches on the tree until it is older and the bark has become tougher.
Never believe that if a little fertilizer is good, a lot is better! Too much fertilizer can cause damage to the leaves. Excessive amounts of fertilizer can cause the leaves edges to turn brown and crisp. Also, beware of using any type of “weed and feed” fertilizers within the root zone area of the tree. These products contain a broadleaf herbicide and can result in the leaves being distorted, and having brown edges.
Do not top trees. Pruning the tops out of trees permanently disfigures the tree and causes stress that damages the health of the tree, particularly in extreme temperatures. It removes a major portion of the trees ability to produce carbohydrates. The stumps that are left are an invitation to wood boring insects. Water sprouts will develop at the base of the tree causing a maintenance problem and rob nutrients from the top of the tree. Also, the once shaded bark on the tree is now exposed to hot, direct sunlight, causing scalding.
Healthy trees add value to our homes. To protect that investment, we have to become detectives to find out what’s causing our trees to be sick. If you have problems and can’t figure out what is wrong, call your local nursery and ask for a certified nursery professional, or call Texas Cooperative Extension at 210-467-6575 and ask for the Master Gardener. Our volunteers are often able to identify symptoms and offer advice. If you need a tree service company, look in the yellow pages for a certified arborist.
This article was written by Lynn Rawe, County Extension Agent-Horticulture with Texas Cooperative Extension in Bexar County.
