The rose is a symbol of fragrance and loveliness. While it is discouraging to see brown spots on your roses, the condition is treatable. Brown spots on roses are commonly referred to as "black spot."
Excessive heat and periods of drought will cause the edges of rose leaves to turn brown, especially if water droplets are on the leaves of the rose when the sun comes out, the sun will burn the leaves. If holes in the rose leaves accompany brown spots, slugs are the culprit.
If left untreated, brown spots on rose leaves will eventually cause the leaves to fall off. Brown spot can also cause the stem of roses to become weak.
Cut off infected leaves. Using a hose-end sprayer, spray entire rose with a few drops of vegetable oil, 1 tsp baking soda and 2 tsp dish detergent. Apply this spray needs once a week.