The plan has been fertilized a week ago with Scotts Roses and Bloom fertilizer

Could be fertilizer burn. Did you water first, then add ferts, then water again? Is it a powder fert? With ferts, more is NOT better. Counter-intuitive, I know.

I think the brown was there even before I added the fertilizer. The fertilizer is in granules. I did water after adding fertilizer.

Can it be due to lack of enough water in the AZ hot summer?

Looks like salt burn to me.

Since you didn't say wherein AZ you live might I suggest googling rose society meeting and the name of your city to see if a group of rose enthusiasts exist for their advice.

This post was edited by Fascist_Nation on Tue, Jun 17, 14 at 17:21

Go to the rose forum.(above) Post the same picture and you will receive a answer on the rose site. The bloggers there are very knowledgeable and I use them all the time.
Looks just plain burnt from the sun to me.