From: Flocke, Karl <karl.flocke@tfs.tamu.edu>
Sent: Wednesday, February 14, 2024 4:37 PM
To: Susan Smith <susanportersmith@hotmail.com>; JON@ogdenstreeservice.com
Cc: Flocke, Karl <karl.flocke@tfs.tamu.edu>
Subject: Oak Wilt

On February 2^nd, 2024 I performed visual inspections for oak wilt on 13 properties in the Country Estates neighborhood of San Marcos.  Properties were only entered with the explicit permission of the landowner.  I was able to confirm a pattern of mortality and foliar symptoms indicating that the large oak wilt center between Mustang Lane and Palomino Lane has escaped containment trenches in two separate areas.  I was also able to identify a second area of mortality consistent with oak wilt near the intersection of Mustang Lane and Country Estates Drive. 

 I have attached 3 maps of the oak wilt areas (shown in red). 

Map 1

The yellow and black dashed line indicates where I would recommend trenching to maintain a distance of 100 feet from symptomatic trees, while simultaneously following the path of least resistance.  If the trench were placed as indicated it would be approximately 1700 feet long.  The trench could either go all the way around the mortality (to contain the disease), or the trench could be placed on one side, two sides, etc.  Our assessment is that trenches work approximately 70% of the time.  The remainder of the time oak wilt will “breakout” in one or more areas.  Exact placement of the trench can be determined by yourself and the trenching contractor as long as it is at least 100 feet away from oak wilt symptomatic trees.  Trees within the 100-ft barrier, especially those without symptoms, may be uprooted or cut down and removed to improve the barrier.

Trenches that have the ability to contain the oak wilt disease (as drawn on map) are potentially eligible for partial cost-share reimbursement by the Texas A&M Forest Service.  This trench may be eligible for a 40% match with a maximum cap of $4,500.  If you wish to pursue this option, please reach back out to me well in advance of trenching to apply for these funds.  

Map 2

The blue and black dashed lines indicates where I would recommend trenching to maintain a distance of 100 feet from symptomatic trees, while simultaneously following the path of least resistance.  If the trenches were placed as indicated they would be approximately 625 feet and 150 feet long.  The trench could either go all the way around the mortality (to contain the disease), or the trench could be placed on one side, two sides, etc.  Our assessment is that trenches work approximately 70% of the time.  The remainder of the time oak wilt will “breakout” in one or more areas.  Exact placement of the trench can be determined by yourself and the trenching contractor as long as it is at least 100 feet away from oak wilt symptomatic trees.  Trees within the 100-ft barrier, especially those without symptoms, may be uprooted or cut down and removed to improve the barrier.  These trenches would not be eligible for cost share reimbursement because the oak wilt mortality center is left uncontained in another area. 

Map 3

The blue and black dashed lines indicates where I would recommend trenching to maintain a distance of 100 feet from symptomatic trees, while simultaneously following the path of least resistance.  If the trenches were placed as indicated they would be approximately 1100 feet (west trench), 475 feet, and 510 feet long (east trenches).  You may wish to delay the installation of the 510 foot long trench to allow the oak wilt more time to approach the trench zone, potentially increasing its likelihood of success.  The trench could either go all the way around the mortality (to contain the disease), or the trench could be placed on one side, two sides, etc.  Our assessment is that trenches work approximately 70% of the time.  The remainder of the time oak wilt will “breakout” in one or more areas.  Exact placement of the trench can be determined by yourself and the trenching contractor as long as it is at least 100 feet away from oak wilt symptomatic trees.  Trees within the 100-ft barrier, especially those without symptoms, may be uprooted or cut down and removed to improve the barrier.  These trenches would not be eligible for cost share reimbursement because the oak wilt mortality center is still left uncontained in the middle. 

Special Note on Trenching

As discussed during our site visit there has been a long history of trenching in your neighborhood with mixed success.  Over the last 31 years the oak wilt center between Mustang and Palomino Lns has been trenched on four separate occasions for a grand total of approximately 1200 feet.  Including the current breakouts, oak wilt has escaped in approximately seven locations over the years.  This can be viewed as a 100% failure or a 99% success depending on your perspective.  Neighbors need to be aware of this issue and weigh the potential costs and success rates of all treatment actions (and inactions) when they make their decisions on how to proceed. 

Injections

Oak trees up to 150 feet away from the symptomatic trees are potential candidates for fungicide injection.  Injecting trees does not stop the spread of the disease, but it can attempt to preserve the canopy of the injected trees.  Often two injections are needed per tree, one now and one 1 ½ to 2 years from now.  There are a few different methods to inject trees, however we recommend “macro injection into the root flare”.  This method is described by going to https://texasoakwilt.org/videos/managing  .  Injections performed with this method are about 80% effective.  If a trench is installed, trees outside of the trench line should not be injected with fungicide. 

The disease can spread about 75 feet per year.  I encourage you to monitor your trees to see if the disease is spreading.  More trees may need to be injected, or the trench location may need to be moved out, as the disease spreads.  Please keep your neighbors informed about the disease so that they may choose to trench or inject before oak wilt reaches their yards.

The https://texasoakwilt.org/getting-help/vendors website will have lists of arborists, injection companies, and trenching companies.

Please let me know if you have any questions. 

Karl Flocke

Woodland Ecologist III

6330 Hwy 290 E, Suite 115

Austin, TX 78723

karl.flocke@tfs.tamu.edu | office 512-339-7807 |fax 512-339-6329

txforestser

Letter-to-Residents.PDF  (you can download this PDF and print