Posts Tagged ‘live oak’

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.

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.

Oak Anthracnose – introduction.

Oak Anthracnose

Perhaps you have noticed your Live Oaks dropping new leaves this spring. The moist conditions of the past winter and early spring, in conjunction with seasonably cool temperatures, has allowed a number of fungal diseases to develop on the leaves of many of our shade trees. One of these more pre

valent this year is Oak Anthracnose. This disease infects the foliage of nearly all Oak species. It is most prevalent in our Live Oaks this year. Although it can cause problems, generally this disease is not a serious threat to the long-term health of the tree.

Oak Anthracnose – symptoms, characteristics and effects.

The spores of the fungus infect young supple leaves just emerging in the spring. After a period of rapid infection, the leaves begin to fall. Symptoms are evident on a portion of the leaf and are expressed by the margin of the new leaf turning brown or becoming necrotic. This area of browning is usually along one of the leaf margins, causing the leaf to become curled and fall to the ground. Not all infected leaves fall. In fact, many will remain on the tree throughout the season causing the overall appearance of the tree to look a bit odd. Trees in areas of little air movement and those with thick, dense foliage are most readily infected. The lower, inside canopy usually exhibits the most intense symptoms, as these leaves dry more slowly.

Temperatures consistently over 80-85 degrees Fahrenheit cause the infection cycle to cease. Fortunately, the portions of the canopy that drop leaves, will produce new leaves. Single year infections rarely cause much damage to the tree. If the disease repeats next season and infects a larger portion of the tree, preventative fungicide applications may be needed. Foliar sprays, which reduce the incidence of the disease, should begin when the new leaves appear in March. It usually requires 2-3 applications at 21-30 day intervals to adequately manage this disease. If evidence of the disease is observed in late spring or early summer, foliar sprays are normally not recommended. Your arborist may however, recommend deep root fertilization in order to encourage the production of new leaves and improve the overall health and vigor of the tree.

Of course, if you have any further questions regarding Oak Anthracnose, Live Oaks, or trees in general, we are here for you.