San Diego County, California

Willow Trees Update

May 2017

Wired magazine article about the polyphagous shot hole borer beetle and the Fusarium dieback – ‘All the Trees Will Die, and Then So Will You


February 1, 2017

The mystery of the arroyo willow dieback along Escondido Creek continues, but our message remains the same – please do not move any cuttings from the infested areas. TECC recently received an update from the samples collected in December by Dr. Eskalen from UC Riverside.  Four fungal pathogens were identified.

“These fungi are known to cause wood canker and dieback on a wide variety host trees worldwide. They are also known to produce overwintering structures where they release spores the following spring to “reinfect” its host plant and possibly spread to others. Therefore, further studies need to be done on the epidemiology of this new disease of willow in Escondido Creek.”

We will continue to monitor the willows throughout spring.

For photos and to read the complete lab report, go to:


December 15, 2016

Recently, the mystery of our diseased willow trees has been in the media. If you recall, back in June, we noticed than many willow trees along the Escondido Creek in Elfin Forest were showing signs of a sudden die-off.  The trees changed from healthy in appearance to wilting with blackened leaves in just a few weeks. Initially the culprit was thought to be the Kuroshio Shot Hole Borer beetle, but test results from the lab at UC Riverside came back negative. After sending a second set of samples to the lab, a different fungus called Phaeoacremonium was found. The mystery continued, because this fungus is usually very slow-growing and not responsible for sudden die-offs.

Dr. Eskalen from the lab in Riverside made a visit to our infected willow trees in early December to examine and take samples. Those samples are with the lab and we are awaiting results. We continue to ask those who visit these trails to please stay on the trails, keep dogs on a leash, and do not collect or move firewood.  More information about the role of firewood in spreading invasive pests can be found at

Below are the three recent articles/videos about the mystery disease damaging our willows.

San Diego Union-Tribune, “Mysterious willow die-off at Escondido Creek”:

10News – San Diego, “Mystery Disease Ravaging Willows in Elfin Forest”:

The CW6 San Diego, “Mysterious disease damages willow trees along Escondido Creek Watershed”:

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