Ah ha! Counterintuitive on not watering but the scarring part makes sense. Will keep my eye out for other trees to try it on, would love a little Joshua tree forest. Thanks for the advice.
http://bugguide.net/images/cache/YRI/QCR/YRIQCR7Q9R90OQ40JQM...
The larvae of this weevil can make burrows in the Joshua Tree and eventually kill your tree.