Two Years of Record Temperatures Taking Their Toll

Spider Mites

Suffering North Texas Trees

The Summer of 1998

Pathologists Corner, Jan 1998

Pathologists Corner, Jan 1997

Look for Your Root Flare

Important Landscape Information and Strategies

Dormant Season Tree Care

     The 1998 and 1999 summers in North Texas have been brutal on our shade trees, both native and introduced.  One key impact is that we have seen established Shumard and Texas Red Oaks fail to re-leaf this year.  Some of these trees are on irrigated sites in well cared for gardens.

     It appears that high soil temperatures during the last two years have damaged the root systems of these species resulting in death or significant dieback of the tree.  Many of these formed buds for this year's growth, last fall, then went into dormancy as normal, but failed to leaf out this year.  We have ruled out most pathological reasons that might have caused the mortality.  These are Red Oaks that have not sustained any type of root injury or change in their root environment.  What is interesting about each of these particular trees is that not one was on a consistent deep root fertilization program before it died.  Another example of the potential benefits in the proactive care of trees.

     Many of our customers utilize our customized blend of high quality organic fertilizer in their maintenance program.  The high-pressure soil injection process aerates the soil while surrounding the main root system with our special mix.  The effectiveness of the system is quite impressive, particularly when utilized in areas with distressed trees, or even worse, those damaged by construction.

     The fertilizer material has a high humate content, along with a micronutrient complex and beneficial soil borne bacteria.  This material does not promote excessive top growth, as many high nitrogen materials will.  It does however, promote a healthy environment in and around the root zone of trees stimulating the natural biological systems.  As mentioned, the application process helps aerate the root zone.  This is critical in our heavy clay soils of North Texas, as tree roots are opportunistic growers in well-aerated soils.  Root invigoration programs can be designed on a remedial basis if we are working with damaged trees or a maintenance basis once or twice a year.

     Of course, anyone interested in more information about our deep root fertilization program can contact an Arborist at our office.

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     Spider mites are a pest that attack a wide variety of our shade trees and landscape plant material.

     Mites are technically not an insect but more closely related to ticks or spiders.  They are extremely small and difficult to see with the naked eye.  The damage, however, is fairly easy to spot once you become familiar with the symptoms that spider mites produce.

     A flecking or stippling appearance on the top side of foliage of affected plant material is the most common symptom produced by spider mites.  Often a dusty or gray cast is apparent on damaged foliage.  Many of the warm season mites produce toxins during feeding on plant tissue, which can cause yellowing and leaf drop when populations are high.  Spider mites have a short life cycle and reproduce every 5 (five) days.  Often all stages from eggs to adult are present at any one time.

     Daytime temperatures over 75 degrees are favorable for spider mite activity and reproduction.  In the north Texas area, we normally experience mite activity from May through September.  Early control measures, prior to the development of wide spread visual damage, is critical.

     Mites will commonly over-winter on trees and shrubs.  Over-wintering populations can be greatly reduced with dormant oil applications.  This manages the mites present on the plant at the time of application and helps reduce early season outbreaks.  Additional control measures are necessary with approved miticides.  A series of spray applications are made from May through August to assure good control.

     Trees and shrubs in our area which are commonly attacked by spider mites include:  Bald Cypress, Live Oak, Cedar Elm, Magnolia, Althea, Azalea, and Boxwood.

     Contact your Arborist for more information and  pricing of our spray programs.

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     We are experiencing the hottest weather we have had in nearly two decades.  Not only are the temperatures high, but they have been constant as well.  This has taken its toll on our landscapes and especially our trees.  Many of the tree species which are not well adapted are failing.  Many of these have been planted since the last time we experienced temperatures like this, nearly 18 years ago.

     It appears that Mother Nature is cleaning up the exotic taste of many of our Landscape Architects.  Birch, exotic Maples, Cherries and many others are fading away.  This is a good lesson to learn from.  We so often look only at "plant hardiness", a rating which predicts how low of a temperature a plant can tolerate without substantial winter injury.  Unfortunately, there is really not a rating for heat tolerance.  This is leading to some substantial plant loss throughout the Metroplex.

     The species of trees which we have recommended to avoid, Silver Maple for example, are failing in high numbers.  The high air temperatures have raised the average soil temperature above our norm as well.  This can accelerate the onset of soil borne pathogens.

     The biggest mistake we are seeing is that homeowners are trying to compensate for the heat by increasing the irrigation frequency and output.  Many times this will cause irreversible damage to the root systems of existing trees which can lead to failure in the future.  It is certain that irrigation systems need to be adjusted, but please do not overdo.  It is difficult to provide a recommendation for all properties because there are so many variables when it comes to a specific site and water needs.  In general our soils absorb water slowly, therefore, high volume irrigation systems deliver too much water too fast, resulting in runoff and waste.  Ideal irrigation would thoroughly wet the soil to a depth of at least one foot.  Deep, slow irrigation once or twice a week is preferable to daily, light irrigation.  One promotes deeply rooted, healthy plants equipped to deal with the worst Texas weather, and the other produces shallow rooted plants which readily exhibit the problems associated with drought conditions.

     There are a few telltale signs to look for around the landscape which can indicate too much water.  The first is a green sheen on the soil surface indicating algae growth.  This green color can also be seen at the base of foundations and on stone work.  The second sign would be moisture seeping from the edges of walks and curbs.  If you see any of these signs, your trees are likely suffering from too much water and you should take steps to reduce irrigation frequency and output.

     If you have any questions regarding this or any other topic we cover, please contact your Arborist. 

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     Oak wilt is caused by a fungus (Ceratocystis fagacearum) which colonizes the vascular system of the tree.  Conduction of water is disrupted causing the leaves to wilt and ultimately for the tree to die.  The disease is highly virulent and spreads in two (2) known ways.  Trees which have formed root grafts with infected trees may themselves become infected through root graft transmission.  For this reason entire stands of Oak forests may be destroyed over a period of time.  New Oak wilt infection centers may begin when a small sap feeding beetle (aka Nitidulid) visits a spore mat on an infected Red Oak.  (Live Oaks do not produce spore mats).  Once the insect has visited a spore mat, his body may carry the fungal spores to a fresh wound, thus creating a new Oak wilt center infection.  The sap feeding beetles are attracted to feed on the sap which oozes from fresh wounds on trees.  Sap feeding beetle activity, spore formation and tree susceptibility are all at high levels from February to June.  For these reasons the Oak wilt control strategy involves the following recommendations:

1. Avoid pruning mid February - mid June (Red Oaks and Live Oaks).
2. If you must prune during this time, paint cuts and wounds as soon as possible after they occur.  The sap flow from wounds usually has stopped within 24-48 hours, therefore, old wounds do not require painting.
3. Healthy trees near Oak wilt infection centers may be treated on a preventable basis with the fungicide "Propaconizol" (aka Alamo).  This fungicide is injected into the tree at the root flares, and can protect trees for up to three (3) years.
4. Once trees have become infected, successful therapeutic treatment with Alamo is possible, however, results vary and most trees will not survive once symptoms develop.
5. Infected trees, particularly Red Oaks, should be removed promptly.  Red Oak firewood may be another means by which the fungus may be transported to new areas.

     Additional research is needed to solve the biology regarding the overland transmission of this potentially devastating tree disease.

     More information is available concerning Oak wilt through the Texas A&M extension service, the Texas Forest Service or on the internet at:  http://Cygnus.tamu.edu/texlab/oakwilt.html

     If you have any further questions or suspect you may have Oak wilt please give us a call. 

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     The root flare is the portion to the tree where the trunk widens at the base as it transitions to the root system.  This flare occurs at the natural grade of the soil.  It is of critical importance that this level be maintained.  The addition of soil around the base of a tree is extremely damaging as trunk tissue deteriorates slowly when in constant contact with soil and soil moisture.  The critical tissue damaged is the phloem which is responsible for the distribution of food energy manufactured in the  leaves.  As the phloem deteriorates, the tree looses its ability to utilize food energy for growth.  The result is a tree with poor growth, die-back, and eventually, death.  The problem is easy to diagnose.  Examine the base of the tree.  If there is no obvious widening as the trunk enters the ground, then the tree is not at its natural grade.  Remedial action may be necessary if this is the case.

     Remedial action involves careful excavation of the excess fill, removal of girdling roots, and in some cases, the construction of a tree well.  Lack of rot flares occur when the trees are planted too deeply, when landscape additions such as flower beds are added around existing trees, or during construction.

     I see far too many trees suffering from problems related to improper grade.  In many cases remedial action can help these trees.

     As always, our staff is ready to help your trees be their best. 

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1. It's time to prune Oaks - especially Live Oaks and Red Oaks.  To avoid the chance of your trees contracting Oak Wilt disease, necessary pruning should be done before February 1, 1995.  The risky and inappropriate time for Oak pruning is February 1 through June 15.  (According to Texas Forest Service).



2. For the best root development, aerification is the key.  Our deep root invigoration process helps considerably with aeration as well as providing your trees with the nutrients required for good growth in our soils.  Fertilization and inspection programs are available.



3. Turf grass and Trees ........ As most of you know, it is extremely difficult to have both beautiful, healthy trees  and a wonderful lawn.  These two types of plants are inherently incompatible.

     Trees originated in forests with rich, fertile soils and surface layers covered with decomposing leaves and other organic material.  Yet in many of our landscapes we attempt to grow trees in compacted, disturbed soils with aggressive turf grass competition over the entire root zone.  This competition with grass along with the absence of a humus layer, restricts the development of the absorbing fine roots.  Further, mowing and weed management also lead to tree problems; mechanical bark damage from line trimmers and mowers, as well as the use of herbicides, can cause severe damage to trees whose roots are within the treated area.  Although herbicides that can cause tree damage have precautionary statements on their labels, most applicators do not realize that tree roots extend 2-3 times the branch system.  Therefore, herbicide injury is a frequent occurrence.  Trees cause problems for the grass.  Excessive shade limits photosynthesis and the subsequent production of carbohydrates necessary for turf growth.  Most turf grasses do well in full sun, may tolerate partial shade, and barely survive in heavy shade.

SOLUTIONS:

     The most effective strategy to improve conditions for trees is to maintain large, mulched areas around them.  Eliminate grass and use mulch.  A shade tolerant ground cover such as Vinca, English Ivy, Moneywort, or others, can then be introduced into the mulched area, if desired.

     For small trees the mulch area should extend to the drip line.  Dramatic growth response can be expected because the mulch improves aeration in the upper portions of the soil, improves water retention and moderates soil temperatures, further, as the mulch decomposes, nutrients become available to the tree.

     Tree-Turf conflicts will always be with us, however, beautiful landscapes are attainable if we use the right plants in locations and environments in which they are best suited. 

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     This column is devoted to subjects relative to tree health, common problems encountered, and tips which will help you help your trees.

     Although the deciduous trees have lost their leaves for the winter and we humans consider the trees to be dormant, physiologically the tree is very active.  New roots are being developed and the tree is preparing itself for the upcoming spring.  It is important to note that photosynthesis may have stopped when the leaves drop, however, respiration does not.  Respiration is the process where food manufactured in the leaves is burned with oxygen obtained through the roots to provide the energy necessary for growth.

     What's the point?  The past several winters have been extremely wet with the soil saturated for long periods of time resulting in low oxygen levels in the soil and consequently a low rate of respiration.  Many of our tree species which prefer a dry site (Texas Red Oak, Chinquapin Oak, etc.) have experienced some problems related to weakened root systems that I believe to be caused by the excess water and low oxygen levels in the soil.

     What can I do?  Although no person can control the weather, each of us can control the use of our irrigation system.  Our clay soil should be allowed to cycle through wet and dry periods.  Prior to irrigation check the soil at a depth of 6 to 8 inches.  If it crumbles, it is time to irrigate.  If it packs into a wet clay ball suitable for making pottery, no irrigation is necessary.  Allowing the soil to dry increases the oxygen content and then the respiration rate.  You will have healthier, stronger plants able to withstand our hot Texas summers, if you irrigate less frequently, but thoroughly saturate the root zone when you do irrigate.  The benefits are stronger roots, healthier plants and a lower water bill.

     The dormant season is an excellent time for tree pruning.  Live Oaks and Red Oaks should be pruned at this time or in the heat of summer to cut down on the risk of Oak Wilt disease.  Live Oaks and Red Oaks should not be pruned in the spring.

     If you have any questions concerning the health of your trees, please call us.  One of our Certified Arborists will be happy to answer your questions. 

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