Where you at and how much rain have you had this summer? Looks like it could just be typical late summer leaf burn. It's been bone dry for a while in my neck of the woods.

It’s barnacle scale aka wax scale... finally found pics of it. The yellowed leaves are secondary to the scale infestation. It was literally covering all the stems of the plant.

http://nathistoc.bio.uci.edu/hemipt/Ceroplastes%20cirripediformis.htm

I'm not familiar with barnacle scale specifically, but the scales I do know can be sprayed with light horticultural oil to smother the scale insects. Here is a link to a more thorough discussion.

http://ipm.ucanr.edu/PMG/PESTNOTES/pn7408.html