Over recent years, oak wilt has devastated a significant number of oak trees in Austin, Texas. This disease essentially clogs the water-conducting system of an oak tree, thereby depriving the tree of water. Without this key component of nourishment, the tree succumbs to death. Since there are several tree diseases that are similar to oak wilt, it is important to verify that the disease of an affected tree is in fact oak wilt. An arborist can likely validate the diagnosis of oak wilt simply based on the symptoms noted while in the field. However, if certainty remains questionable, the most indisputable method for confirming the disease is through professional laboratory testing.
Samples of oak must first be collected from a suspected diseased tree. To do this, first identify branches that are partially wilted. It is important that the selected branches not be completely wilted, dry, or dead or the laboratory testing may be ineffective. The leaves on the branch must be identified as symptomatic. For red and white oaks, this includes leaves that display a pattern of wilt from the margins inward toward the trunk of the oak. For live oaks, this includes leaves that display veinal necrosis, yellowed veins that eventually turn brown due to wilt and subsequent death. Once identified, collect a sample of the affected leaves, and place each in a resealable plastic bag.
The wilted tree branches themselves may also offer valuable diagnostic information. By examining a cross-sectional view of a branch, the presentation of sapwood discoloration is an excellent indicator of the presence of oak wilt. A longitudinal section may be necessary for the examination of red oaks. To examine a cross-sectional or a longitudinal section view, the bark must carefully be removed from the wilted branch. If discoloration is not noted in a particular area of the branch, it may be necessary to examine yet another section. It is important, however, not to remove all of the bark, as sections of the branch which include the bark may also be sent in for laboratory testing.
To submit branch samples for testing, select samples from as many as three symptomatic branches per tree. It is essential that the sapwood must be palpably moist and the inner bark alive and green. This may be checked by removing a small section of the outer bark. It is also essential that each sample be at least one inch in diameter and cut in a length of six to eight inches. Store the samples in a resealable plastic bag, and be certain that samples from each symptomatic tree are stored separately of one another. Consult an Austin tree trimming specialist for assistance if you have any questions or concerns regarding the appropriate collection and storage of samples.
Samples collected in the field should be stored in a cool place, should never be exposed to direct sunlight, and should never be exposed to temperatures exceeding 90 degrees. Samples should also be mailed overnight delivery or delivered in person to the laboratory if possible. It is also advisable to send the samples early in the week in order to avoid delivery on the weekend and so that the testing can occur before the end of the work week. Samples should remain in the resealable plastic bags in which they were placed when collected in the field. Then, they should be mailed or delivered in a disposable ice chest with sufficient ice packs to keep the samples cool, moist, and viable.
If you suspect an oak is affected by oak wilt, consult an Austin tree care professional for further assistance.
About the Author: Andrew Johnson is the owner of Central Texas Tree Care, a leading provider of Austin tree service in Central Texas. Certified ISA Austin arborist services including: tree trimming, tree removal, tree care and oak wilt treatment. For more information on Austin tree service, please visit https://centraltexastr.wpengine.com.