Most tree problems (an estimated 85-90%) result from environmental or other stressors rather than from disease or insects. Probably the two most common problems we see while visiting homeowners are underwatering and planting too deeply. These conditions cause abiotic or cultural problems for trees.
Environmental stress is cumulative – if there are drought conditions and then insects attack, the tree may not survive the accumulated stress. Texas trees were incredibly stressed by five years of drought beginning in 2010 (the Texas Forest Service estimated that we lost more than 300,000,000 trees in the state), and the past two seasons have been wetter than normal. Trees are continuing to die from the drought and, recently, too much water.
This year (2016) we have seen several examples of cumulative stress on post oaks resulting in sudden death or defoliation. That condition was recently the subject of the Texas Plant Disease Diagnostic Lab’s blog post. Read more here:
Conditions that are stressful to trees
- Construction damage: A tree’s roots extend horizontally approximately double the height of the tree. For example, if a pool is added, and the contractor puts a fence 5’ away from the trunk of a tree, don’t be surprised if the tree begins to drop leaves or turn color. It can take years for a tree’s roots to recover from being disturbed.
- Too little water: Trees need water to survive. If your grass is green and healthy, the trees will probably be okay. If it is a new tree, give it extra care while the root system is establishing. See the section on Tree Planting for more specific information. http://txmg.org/denton/north-texas-gardening/trees/how-to-plant-a-tree/
- Too much water: Post oaks, in particular, do not like wet feet! They are adapted to our normally dry conditions. It is difficult to mix St. Augustine grass with post oaks because keeping the grass happy keeps the soil too moist for post oaks.
- Herbicides: One step products that promise to kill weeds while fertilizing contain herbicides. That’s the “weed” part of weed and feed. You can overdo it, and it can seriously damage trees. If you choose to use these products, be sure to follow the label directions. Twice as much is a very bad idea.
- Too much sun for shade lovers or too little sun for those that need it.
The following are examples of trees damaged by various environmental conditions:
Figure 1: This tree’s roots are girdling and killing the tree. Trees growing in confined spaces, such as pots, containerized planters, or small concrete soil cutouts located in parking lots or sidewalks; trees forced into small planting holes where the roots are twisted as planted; & trees planted in compact soil can form circling root systems.
Note: don’t forget to remove any wrapping that may come with a new tree because that can also girdle the tree. (Texas Forest Service: “Correcting Circling or Girdling Tree Roots”) This is not something a homeowner can tackle. Call a certified arborist.
Figure 2: Damage from lawn equipment. One good reason to remove grass around the tree is to prevent damage from weed eaters and lawn mowers.
Figure 3: Lightening damage leaves a wound that may go the entire height of the tree. It often has a burned appearance. Wind, hail and extreme cold can also damage trees.
Figure 4: Planting too deeply is extremely common and, over time, causes the tree to die. If it looks like a fence post, it’s too deep! For proper planting instructions, go here: http://txmg.org/denton/north-texas-gardening/trees/how-to-plant-a-tree/.
See also Texas Forest Service recommended planting steps.
Figure 5: Sunscald or sunburn usually occurs on the southwest side of new thin-barked trees, such as fruit trees, maple and ash. It happens because trees are crowded in the nursery and never have their bark exposed to the sun; then it is planted in full sun and it burns. To prevent sunscald, wrap the trunk for the first summer. More information on sunscald damage from Washington State University Extension.
Texas Plant Disease Diagnostic Lab. Retrieved from http://plantclinic.tamu.edu/2015/09/18/stress-canker/ and http://plantclinic.tamu.edu/category/abiotic/