What are the Texas Hill Country Concerns?

Severe Drought Conditions

Extreme drought conditions will undoubtedly have adverse effects on the trees that exist in the area. Trees lose significant amounts of water directly through the leaves, twigs, branches, roots, and stems. Trees will react in a variety of ways. One of the effects of a severe drought is that permanent damage can occur. Here is a list of how trees are affected by severe drought and ways to reduce drought stress.

Effects and symptoms of drought stress in trees:

  • Wilting- this is a visible symptom of drought. Permanently wilted trees can recover only when additional water is added.
  • Stomatal Closure- Trees close stomata in response to rapid water loss, but this will not prevent water loss. A significant amount of water is lost through twigs, branches, roots, and stems.
  • Early Leaf Shedding- Premature senescence and shedding of leaves are induced by drought stress. In a severe drought situation, leaves may be shed while still full of valuable materials.
  • Effects on Photosynthesis- The reduction of photosynthesis is a major effect of drought and carbohydrate stores are being reduced. Considerable time is needed for photosynthesis to operate in pre-drought conditions.
  • Growth Inhibitions- Shoot, cambial, and root growth are all negatively affected by drought conditions
  • Biological Leg Effects- Trees have a lag time before normal processes are established. Trees can show the effects of a severe drought for 2-3 years after the drought has occurred
  • Pest Problems- Drought predisposes trees to pests and diseases due to low food reserves and poor response to insect and disease attacks. Drought creates unhealthy trees.
  • Visible Symptoms- Deciduous trees show curling, rolling, mottling, scorching, chlorosis, and early shedding of leaves. As drought intensifies dieback of twigs and branches in the tree crowns will occur.

How to reduce drought stress:

  • Prevents soil compaction by reducing heavy vehicle traffic or restricting such traffic to designated areas.
  • Reduce/remove competing vegetation, especially around young trees.
  • Plant trees that are well suited to your site (use local native species).
  • Apply mulch around newly planted trees.
  • Remove any weed fabric, decorative rock, etc from around the tree as far as you can go. Roots need room to breathe and grow too! Replacing with mulch helps keep moisture around the tree.
  • During extreme drought, do not fertilize trees. Fertilizers do more harm than good.

Oak Wilt

Oak wilt is a devastating tree disease caused by the fungus Bretiziella fagacearum. This disease is one of the biggest causes of oak tree death in the Hill Country. Oak wilt can be spread both underground and above ground. If an infected beetle lands on a freshly pruned cut, it can infect the tree. Oak wilt can also be spread through root grafting. If oak tree roots have grafted together then the disease can spread from tree to tree. Oak wilt can move at a rate of 50-100 feet per year through root grafting. Most oak trees infected with oak wilt die within a few months. Oak wilt is easy to prevent and very difficult to treat.


When pruning oaks be sure to do it at the right time of year. The best time to prune is the hottest and coldest months of the year. Sterilizing your equipment before and between each tree is very important in preventing the spread of diseases. Painting over a cut wound should be done immediately after pruning the tree so the pheromones don’t attract disease-carrying beetles. If you see suckers on the trees they shouldn’t be removed because they are needed to heal wounds and vigor.


Anthracnose is a disease that can be mistaken as oak wilt easily. One of the easiest ways to distinguish the difference between the two is that oak wilt starts at the top of the canopy and anthracnose starts at the lower and inside of the tree where the humidity is highest. A fungus, Apiognomonia quercinia, causes oak anthracnose. The fungus affects the buds, leaves, or twigs. The leaves may begin to develop brown spots and patches. Some leaves even start to become misshaped. During the winter the fungus lies dormant in the infected leaves, but in the springtime, the spores become airborne and infect the new leaves coming on. Anthracnose thrives in moist and warm conditions and can be spread by watering and rain. The best way to control anthracnose is to rake up the dead, moist leaves during the fall and winter months along with pruning the dead and dying branches.

Sudden Oak Death

Sudden Oak Death (SOD) is caused by the plant pathogen Phytophthora ramorum. One of the first symptoms that appear is bleeding or oozing of dark reddish-brown thick sap. It is called SOD because of the rapid (2-4 weeks) browning of leaves without any prolonged visible decline. Even though the death comes unexpectedly the tree could have been infected for more than 2 years before the sudden death. There are a few different ways to test the tree to see if it has been infected. Foliar samples along with bark samples can be sent in for analysis. Injecting the trees with Phosphite can provide the tree with 3-5 years of protection.

Root Rot

Cotton Root Rot

Cotton root rot is a fungus that can live for years in soil and can kill even large trees. It is most prevalent in the summer months. When a tree or plant gets cotton root rot it begins to wilt and experience foliar color changes from green to yellow to bronze. Plant or tree death comes fairly sudden during warm weather but during cooler weather, the decline is slowed down once the warm weather hits it will die. The best way to prevent cotton root rot is to purchase resistant plants or plants that are resistant to cotton root rot.

Phytophthora Root Rot

Phytophthora is most commonly found in soils that are poorly drained or excessively irrigated. Early signs of phytophthora look similar to a drought-stressed plant even though it is overwatered. Some plants may wilt and die from water stress during the first sign of warm weather, but other times it can take several years. Leaves may start to appear dull or fade to yellow, red, or purple. In some cases, a tree can be saved by removing the soil from around the base of the tree down to the top of the main roots and cutting away any bark that is oozy or dark. This leaves the root system exposed and allows the root system to dry completely which slows the spread of Phytophthora.

Construction Damage

Construction damage is one of the leading causes of tree decline or death. Trees you want to keep on your property should be fenced off and all building materials and equipment kept away.

Soil Compaction

Tree roots do not grow in soil; they grow in the spaces between the soil particles. As the soil becomes compacted, those spaces shrink and root growth is inhibited. Roots grow shorter, thicker and have less surface area, and are unable to absorb adequate nutrients and moisture, resulting in lower shoot density, a reduction in carbohydrate reserves, and less drought resistance. Water that is trapped in compacted soil has difficulty moving up through the soil surface where it can evaporate and reduce the soil’s temperature. Instead, this soil water can heat up from the increased thermal conductivity of the denser soil and begin to poach the tree roots. Compaction can result in a significant reduction in the rate at which rainwater from irrigation can penetrate the soil’s surface. Soil compaction occurs when soil particles are pressed together, reducing pore space between them. Heavily compacted soils contain few large pores and have a reduced rate of both water infiltration and drainage from the compacted layer. This occurs because large pores are the most effective in moving water through the soil when it is saturated. In addition, the exchange of gases slows down in compacted soils, causing an increase in the likelihood of aeration-related problems. Finally, soil compaction increases soil strength-the ability of soil to resist being moved by an applied force-a compacted soil also means that roots must exert greater force to penetrate the compacted layer.

Root Cutting

Digging, grading, and trenching associated with construction and underground utility installation can be quite damaging to roots. A tree’s root system can extend horizontally at a distance of 1-3 times greater than the height of a tree. It is important to cut as far away from a tree as possible to prevent damage that can compromise tree health and stability. Cutting under a tree’s crown can reduce tree vitality. Cutting roots close to the trunk severely damage a tree and limit its ability to stay upright in storms.

Smothering Roots by Adding Soil

The majority of fine water-and-mineral-absorbing roots are in the upper 6-12 inches of soil where oxygen and moisture levels tend to be best suited for growth. Even a few inches of soil piled over the root system to change the grade can smother fine roots and eventually lead to larger root death.

Exposure to the Elements

Trees in a forest grow as a community, protecting each other from the elements. The trees grow tall with long, straight trunks and high canopies. Removing neighboring trees during construction exposes the remaining tree to increased sunlight and wind, which may lead to sunscald or breakage of limbs and stems


Webworms (Hyphantria cunea) usually appear on trees in the fall time. They begin as caterpillars that create webbing around tree foliage while eating the leaves. This causes stress and leaf loss on the plant. The caterpillars turn to moths that in turn lay more eggs in the springtime. Over time the webworm can stress the tree enough that it can become susceptible to drought and diseases. One way to get rid of webworms is by removing the leaves that contain eggs by knocking the webs out of the branches. Always knock them into a bag or bucket. Knocking them to the ground will not get rid of them. Some other ways to control the infestation are by planning sunflowers to attract wasps or hanging bird feeders near the area. Both these predators will feed on the caterpillars. One other way to control them is by using BT spray, which infects the caterpillars. BT spray is not harmful to animals or plants like some pesticides but it can lower the population of butterflies in the area.

Iron Chlorosis

Iron Chlorosis is caused by iron deficiency that causes the yellowing of plant leaves. In more severe cases of iron chlorosis, the entire leaf can turn yellow or even white and the outer edges may scorch and turn brown. When the leaves turn yellow it means there is a lack of chlorophyll. With the reduction of chlorophyll plant growth and vigor are reduced. Iron chlorosis occurs mostly in soils that are alkaline and soil that contains lime. Even if the soil has plenty of iron, the high soil pH can cause chemical reactions that make the iron solid, which makes it unavailable for the plant roots. Injections of ammonium citrate or iron sulfate can be used to help -deficient trees.

Emerald Ash Borer (EAB)

The Emerald Ash Borer (EAB) is a very destructive wood-boring pest to ash trees. The EAB is extremely aggressive and can kill ash trees within 2-3 years after becoming infested. The EAB will weaken the tree during the winter and then kill the tree during the summer. The female EAB lays eggs in the bark crevices and then the larvae feed underneath the bark until they emerge from the tree as adults 1-2 years later. The EAB has recently made its way to Texas but has not yet made its way to the TX Hill Country. That being said the EAB can spread at a rate of 1.5-49 miles a year and that is without the help of people moving infested firewood from place to place. Some things to keep an eye out for are:
  • Dead branches near the top of the tree
  • Leafy shoots sprouting from the trunk
  • Bark splits exposing larval galleries
  • Extensive woodpecker activity
  • D-shaped exit holes
Injecting ash trees with the right insecticide helps prevent and treat trees of EAB. If there are infested trees within 15 miles of your trees then you should consider treating your trees preventatively. Injecting the insecticide every 2 years is the best way to protect your trees from getting infested in the future. If your tree has already been infested for a long period then there is a chance the tree can’t be saved. If you notice more than 50% canopy thinning then the tree is most likely not going to.

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