I would go with sun burn. It always happens to me until I finally quit listening to people that claim full sun for tridents. Maybe up north, but down here shade is a must. I put them into all day shade when the temps hit 90.
I did not do the smoke method. I had a club meeting and a horticulture guru that weekend. It was a combination of shallow pot, root bound, and fungus attacking the new growth (cured by daconil).
The shallow showpot and rootbound was just letting the wind dry the mature leaves edges out and the fungus was killing the new growth. All the growth that pushed after the daconil (before repot) pushed green.