I would guess fertilizer on the leaves in bright sunlight. Or in too hot a greenhouse. Considering much of the country warmed up too early this spring, feeding schedules probably did not take into account the unexpected warm temps.
It's hard for us to keep plants fed properly when temps don't fall below 90 for weeks at a time. That may be what happened to the roses.
Just a guess. Roses around here look like the pic on the left quite often, and I see workers spraying the plants with water still connected to the fertilizer pump.
