Noninfectious Diseases of Trees

There are many reasons a tree begins to weaken, wither and potentially dies that have nothing to do with disease. Extreme temperature changes and water supply are the primary cause of tree problems. Secondarily would be chemical substances in the soil, water or air, transplant shock and injury.

So what are the ways a tree can become weakened?

1. Hot or High Temperatures - Hot temperatures can cause trees to defoliate and their leaves to become scorched. Heat or drying winds cause a rapid loss of water. When leaves begin to turn yellow or brown and fall prematurely, it is most likely due to heat.



2. Cold Temperatures - In early fall or late spring, when trees are actively growing, trees are susceptible to extreme cold and frost. Signs of cold weather injury include Frost Crack, where long vertical bulges or cracks are caused in the bark of a tree. Frost cracking can reoccur in the same place causing a buildup of tissues and formations of scarring. To protect your trees in the winter you can do the following:

• Plant tree species adapted to local conditions.
• Cover young trees if frost is expected.
• Avoid planting in low-lying areas subject to frost.
• Do not use high nitrogen fertilizer late in the growing season.
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Avoid wounds to the trunk and properly prune branches to prevent the formation of frost cracks.

3. Drought - Drought occurs when there is a lack of rain over a long period of time. Without an adequate storage of water within the ground the tree cannot uptake water by its roots. Symptoms include wilting, off-color foliage, twig and branch dieback in the crown, and the death of fine roots. The crowns of drought stricken trees usually die from the top down and from the outside in. Trees in this condition are more readily attacked by fungi and insects. Shallow-rooted trees, and trees planted on light, sandy soils with poor moisture-holding capacity are most susceptible to drought. To protect your trees from drought:

• Do not plant shallow-rooted species in areas of low moisture or on sandy soils.
• Put mulch around the base of the tree. In addition to helping retain soil moisture, mulch helps to control weeds, preventing lawnmower and weed whip injury.
• Conifers growing over high water tables for long periods may die quickly after the water table drops. The foliage turns red and drops off soon after death.
• Water ornamental trees about once a week to moisten soil 6 to 12 inches deep into the root zone.

4. Excess Moisture - Trees can get too much water as well as too little. Trees planted in areas where there is poor drainage can become waterlogged. When this happens, oxygen is deprived from the roots and the tree begins to die. Symptoms of oxygen deficiency closely resemble those of drought injury: reduced growth, small leaves and thin crowns, twig and branch dieback, and tree death. Roots in waterlogged soils are susceptible to a variety of soil-borne fungal pathogens. To protect your plants you can:

• Plant species that are adapted to the conditions in areas subject to periodic flooding.
• Prepare planting sites to allow for adequate drainage and root growth.

5. Chemical Injury - There are many chemicals in the air and water that effect trees. Symptoms of chemical injury are often difficult to diagnose, as the possibilities are endless. Some include:

a. Nutrient Deficiency

- Trees need certain nutrients for proper growth. Nitrogen, phosphorous, and potassium are the most important. Symptoms of nutrient deficiency mimic many other diseases and vary greatly depending upon which nutrient is lacking. The most common symptoms of nutrient deficiency are: reduced growth, yellowing, and necrosis.

b. Herbicide Injury

- Herbicides applied improperly can injure trees. Leaves of deciduous trees will become distorted, curled, and brown on the margins. Conifer needles will turn yellow or brown, and succulent shoots will curl or become deformed. Trees will usually survive, but their growth will be stunted.

c. Salt Injury - Salts from roads that is splashed onto the foliage or is absorbed through the roots will cause a browning of the tree, especially on the side facing the roadway. Trees growing where salt accumulates because of drainage patterns will also be affected. The affected foliage will fall off in the spring, thinning the crown, although new growth will make the tree appear otherwise healthy. However, these trees will grow more slowly and remain stunted, and may eventually be killed by prolonged exposure.

There are other noninfectious factors that can cause trees to wither or die including winter scald and other types of pollution. Before treating your trees, be sure to examine all the possibilities. Consult a professional to save yourself time and money and in the long run you may help your tree become healthier.

Andrew Johnson is the owner of Central Texas Tree Care, a leading tree service provider in Central Texas (Travis County and surrounding areas) offering services such as pruning and removals, cabling and bracing as well as arborist reports, diagnostics, pest management, fertilization and Austin tree service trusts. For more information please visit http://www.centraltexastreecare.com.

Tree Stressors and Tree Decline

People aren't the only living thing that can get stressed - trees can too. In fact, tree stress is a serious problem that not only causes significant damage to your trees but also can kill them.

So what causes trees to get stressed? The first is environment. Just like humans, the environment we are surrounded by affects trees. Stressful environmental conditions such as extreme temperatures, poor soil, and physical damage to leaves, bark and roots can predispose a tree to secondary insect and disease attacks. Extremely wet soil can also stress a tree as can soil compaction and freezing.

Trees are also surprisingly affected by other conditions that are caused by man or animal. For example, lawnmowers are one of the major causes of damage to trees. Improper pruning also stresses trees. Too much pruning or pruning during the wrong time of year can harm your tree more than help it. Over watering trees also causes trees great stress, just as flooding or too much rain could. Frequent watering results in roots that are too wet for good growth.

Other human caused stresses are improper handling before planting your tree, construction damage and the use of deicing salts or herbicides. Tree wounds caused by humans can also make your tree quite susceptible to outside influences and therefore make the tree deteriorate over a period of time.

The problem with tree stress is that from the human eye, you may not recognize that your tree is stressed right away. Of course there is obvious stress such as that caused from storms, but the small stresses are also very critical to a trees survival as well. Trees often do not display immediate responses to stresses because of their accumulated growth habit. But when your tree is stressed you will begin to notice that it will change. In some cases, the process of photosynthesis, which is the primary supply of carbohydrates for all tree functions, is reduced and the tree’s stored food reserves are depleted. And if the root systems are also damaged, the tree will be unable to produce sufficient carbohydrates and growth regulating chemicals.

Symptoms of distress will begin to show as your tree deteriorates. The leaves may decrease in number and become smaller in size. Some trees will produce excess fruit or seed - this is its way of trying to survive. Branches will begin to die, and the root system of the tree becomes reduced. From here the tree will continue to decline until the eventual death of the tree, which can take from 2 to 15 years. For many trees, once the decline has reached a certain point, it cannot recover.

If the actual physical stressors to the tree don't kill it, the reduced strength of the tree will leave it vulnerable to disease and insects. The addition of these elements can speed up the trees decline.

Trees in urban areas are often stressed more than those that are in rural areas - this is due to restricted root space, building foundations, streets, driveways and other obstacles that limit the expansion of tree roots and significantly reduce the amount of water and minerals available to the tree. Compacted soils and competition also stresses urban trees.

If you feel your tree has been recently stressed, consult with your local tree professional or arborist for some proactive measures you can take. Trees can be quite resilient and with a little care, they can potentially make a full recovery.


Andrew Johnson is the owner of Central Texas Tree Care, a leading tree service provider in Central Texas (Travis County and surrounding areas) offering services such as pruning and removals, cabling and bracing as well as arborist reports, diagnostics, pest management, fertilization and Austin tree service trusts. For more information please visit http://www.centraltexastreecare.com.