Posts Tagged ‘red oak’

Tree trimmers in April, 2011 work to extend the Red Oak's life.

 GARLAND (CBSDFW.COM) – When you drive down South Garland Road, you can’t help but notice that a piece of Garland history has been stripped away.

“It’s a living witness to all of what’s occurred in this area,” said arborist Steve Houser. “If it could speak, it would tell us some very interesting stories,” added Houser who spent the last five years trying to extend the life of one of the oldest living trees in North Texas.

The once majestic Shumard Red Oak, however, was eventually reduced to a hollow shell after falling victim to a deadly pathogen. “It invades the root system of the tree, travels up to the base and eventually starts to rot and decay the root system,” explained Houser.

At its peak, the tree located at Garland Memorial Park, stood 70 feet tall and its branches spanned 95 feet wide. The Red Oak was designated a champion which means at one point, it was the largest of its kind in the state.

“It was absolutely heartbreaking to lose it,” said Cecil Williams who is president of the Garland-Mills Cemetery Foundation. Williams said he received some 250 phone calls from distraught admirers of the Red Oak when the tree was being cut down. But Williams said he had no other choice. “We could not have it injure or kill anyone. It’s huge and it had cracks that were leaning over toward Garland Road,” he added.

The tree, estimated to be well over 200 years old, was threatening to topple over onto Garland Road. Houser says it might have lived another three years, if not for this summer’s devastating drought.

The tree will be reduced to a three or four-foot high stump with a wood sealer on top, so visitors can count the tree rings or perhaps even sit on it while visiting a loved one buried at the cemetery.

Last month’s article covered basic information about Oak Wilt and its symptoms, along with an introduction to its transmission. The article noted that there is much confusion and misinformation regarding Oak Wilt, and research goes only so far in providing the answers to important questions. Future research will likely change current recommendations — which is a good thing. Early detection and an accurate diagnosis, paired with a solid management plan, are critical to managing the disease successfully. In some cases, there may be a need to develop a management plan for an entire city block or particular part of a community.

Oak Wilt Management/Diagnosis

An Oak Wilt diagnosis can be confirmed in a laboratory by isolating the fungus from diseased tissues. Taking tissue samples is not a simple process and should be left to someone with specific training and experience. Each step of the process must be done properly. Although all the symptoms indicate Oak Wilt is present, lab reports may return as a “negative.” A negative from the lab does not mean the sampled tree is not infected, only that the fungus could not be found in the particular sample provided. Note that “someone with specific training and experience” is typically a consulting arborist, but may also be a forester or Oak Wilt researcher.

Oak Wilt Management/Suppression

Fungal Spore Mat

As previously noted, fungal spore mats form only on species in the Red Oak group and produce a fruity odor that attracts the Nitidulid beetle — believed to be responsible for the overland spread of the disease. As a result, infected and dying red oaks are a greater concern, due to the potential for aiding in the overland spread. There is no evidence that live oaks contribute to the overland spread. The firewood and stumps from removed live oak trees are not a concern.

Since the spore mats have been known to form on stumps and firewood of species in the Red Oak group, infected trees should be promptly removed from the site and chipped, burned or buried. If this is not practical, remove the infected tree’s bark from the soil line up to 2 or 3 feet to help prevent the formation of spore mats. In urban areas, grinding the stump below the soil surface is also recommended.

Avoid storing infected red oak firewood near healthy trees unless it is “seasoned” or completely dried for at least one year. If infected red oak wood must be left on a site, it should be covered with clear plastic and the edges buried in the soil. Avoid purchasing red oak firewood that appears green and not ready to burn. However, burning infected oak firewood of any species will not spread the disease since the heat of the fire will destroy fungal spores.

The disease is most often spread by root-to-root contact. In a dense group of live oaks, Oak Wilt can expand outward to 75 feet or more each year. Trenching between infected and non-infected trees is a method of suppression in a rural setting, but it is difficult and less successful in an urban area due to the number of underground utilities and obstructions.

By comparison, Oak Wilt centers in the DFW area do not appear to be expanding outward as rapidly as centers found in Austin. One theory is that the disease expands more rapidly in communities with indigenous populations of red oak and live oak. These populations have root systems that are more interconnected than an urban forest established primarily by planting new trees. One of the primary indigenous oaks in North Central Texas is post oak (Quercus stellata), which is extremely tolerant of the disease. The same is true for chinquapin oak (Quercus muehlenbergii) and bur oak(Quercus macrocarpa), which should be planted more often for this reason. Are you starting to lose some of your fears yet?

Next month`s article will cover Oak Wilt Management/Pruning. The final article will address Prevention and Treatment. Afterward, we hope to have fewer nervous tree mothers!!

About the author: Steve Houser is a Dallas native with more than 30 years of experience as a consulting arborist. He is the president of Arborilogical Services Inc., “The Experts Your Trees Deserve.”  www.arborilogical.com.

Oak Wilt is a complex disease. To fully explain its impact on our trees will require several consecutive articles. Conflicting information in public venues adds to the current Oak Wilt confusion and creates anxiety or anger over the potential loss of a favorite tree. If Grandpa planted the tree, or it screens the neighbors or reduces your energy bill, the tree has special value. It is no longer just a renewable resource easily replaced. Best not to mess with a Texan’s trees!

Although Oak Wilt research is somewhat limited, a good understanding of what is known offers some level of comfort. Dr. David Appel, professor of plant pathology and microbiology at Texas A&M University, is recognized as an expert on the subject. His research has been peer reviewed, and his guidance helped to develop the standards covered in this article, along with the help of two other plant pathologists with extensive Oak Wilt experience. The disease is not rampant or terrorizing all our neighborhoods. It was first discovered in the DFW area in 1978. Let’s keep things in perspective and rely on those who have worked with, managed, and tracked the spread of the disease as a career.

Oak Wilt and Its Symptoms

Oak Wilt is a vascular wilt disease of oak trees caused by the fungus Ceratocystis fagacearum. The fungus enters the tree and stops the flow of water as well as elements by plugging the vessels in the vascular system. All species of oaks are susceptible, with some species being somewhat tolerant. Red oaks, both Shumard and Spanish, are highly susceptible to the pathogen. Live oaks (Quercus fusiformis and Quercus virginiana) follow as a close second. Oaks in the white oak family such as bur oak (Quercus macrocarpa) or chinquapin oak (Quercus muehlenbergii), are more tolerant of an infection.

In the red oak family, the disease expresses itself in two primary ways. The first symptom is an oily green appearance in sections of the tree’s canopy, which rapidly turns a tan or red color. The second, and less common, expression is a heavy and rapid shedding of foliage with individual leaves displaying the symptoms previously mentioned. Infected red oaks typically die within a few months of infection.

Infected live oaks display a variety of foliar symptoms. The most common is called veinal necrosis, a yellowing/browning of the leaf midrib and side veins.

Affected foliage usually drops as this symptom appears, but it is common for some foliage to remain on the tree. Defoliation of live oak trees can occur at any time of the year, but should not be confused with the normal process of leaf-drop and flowering that generally occurs in February and March. Live oaks typically die within six months of infection, with some individuals not dying for years. Advanced training is required to accurately diagnose and properly treat the disease. Uneducated advice can be very costly.

Oak Wilt Transmission

Oak Wilt most frequently spreads from tree to tree by root-to-root contact. Live oaks regularly form functional root grafts with other live oaks. Red oaks appear to form these grafts as well. Oaks like to be “hooked-up” with each other and swap spit. Kidding aside, once the pathogen has entered one tree, it has the potential to move from tree to tree quite readily and efficiently. Root grafting is known to occur between live oaks and red oaks. This phenomenon is not common, but research indicates the potential exists.

Although infrequent, a second method of disease transmission is by overland spread. This occurs when fungal spore mats are produced on a dying red oak and visited by the suspected insect vector or transmitter, the sap-feeding nitidulid beetle. The beetle can carry the spores to a wound on a nearby tree but the spores can infect the tree only if the wound is fresh and created in the previous 24 to 48 hours. All oaks, including live oaks and species in the red oak family, can be infected by overland spread or root-to-root contact.

It should be noted that fungal mats are produced primarily in the spring or cooler times of the year, and only on infected red oaks in a particular stage of decline. Fungal mats are viable, that is producing spores, for a short period — usually two to three weeks at most. Although new infection centers do form, it is not fully understood whether it is from the insect spreading the disease or other methods of transmission not yet discovered or researched.

If you have questions, remember there is more to follow next month on this thrilling subject!

About the author: Steve Houser is a Dallas native with more than 30 years of experience as a consulting arborist. He is the president of Arborilogical Services Inc., “The Experts Your Trees Deserve.” www.arborilogical.com.

For some trees – it’s not easy to be green.

Avid gardeners know that everything green starts with soil.  Soil is the literal baseline where we begin our horticultural endeavors.  It provides us with our cultural opportunities and constraints.  While we frequently push our landscapes slightly past a soil’s parameters, we often concede to reality. Much of our north central Texas soil is the remnants of a massive blackland prairie that once supported native grasses that grow shoulder high.  We have highly expansive black clay that is derived from the fractured white limestone that lies beneath.  It has always been a mystery that white stone can produce black dirt, but it does.  And, because the soil origin is limestone, the soil’s character is alkaline.

Chlorotic Symptoms on Sweetgum Leaves

Our native trees grow well in our alkaline soils.  That is why they are “native”.  However, as gardeners, we are rarely satisfied with only growing plants, and particularly trees indigenous to our soils.  Nature has provided us with too many beautiful trees to limit our landscapes to a plant palette of strictly natives.  Your local nursery or garden center provides a broad range of “adapted” plants, of which many were introduced hundreds of years ago.

Iron Deficiency in Sweetgum

Part of the gardening ethic is learning that some plants are more adaptive than others are.  This is particularly true with our trees.  We do what we can to modify our soils to accommodate our trees.  We dig an adequate planting hole and add peat moss or compost to the backfill.  We mulch and fertilize with specific additives.  In some urban situations, the native soil is completely replaced by a more suitable media.  As trees grow, we find that all the preparation is not enough.  Sweetgum trees turn yellow when it is not fall, River Birch looks more like River Bleached, and Red Oaks of east Texas provenience appear to be Dead Oaks.

Iron Chlorosis in Red Oak

Interveinal chlorosis is the technical term.  It means the elemental iron that is essential for the manufacture of chlorophyll is not available to the tree.  In mild cases, leaf tissue is light green while the leaf veins remain dark.  In moderate cases, the leaf color is yellow, frequently with brown margins.  The extreme cases display white leaves.

Arborists have a recently introduced tool to address chronic interveinal chlorosis. Verdur® is a form of iron that is immediately available to the tree.  Not only is the green-up rapid, we find a single application relieves the yellowing conditions for about 3 years.  Verdur is applied into the tree’s root flares by a process called macro infusion.  It is a process very similar to that used when treating trees for Oak Wilt.  The tree’s vascular system transports the iron into the canopy where it aids in the manufacture of chlorophyll in leaves.  Green leaves are healthy, energy producing leaves.

Iron Chlorosis in Pin Oak

While Verdur produces excellent aesthetic results, it does not change the origin of the horticultural challenge.  It does not alter the inherent character of your soil.  It bypasses the need for the elemental iron in the soil to be available to the plant.

Verdur is a great tool for treating chlorotic trees that are deemed too large to fail.  We find the most effective time to apply Verdur is during the dormant season (November, December, and January).  Contact your arborist to see if Verdur is appropriate for your trees.

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.