What might look like a fungus on a rose is actually tiny pests. Every year I have a single rose that seems to get eaten alive by these bugs.
Rose Leafhopper Edwardsiana rosae (Linnaeus) (Homoptera: Cicadellidae). This guy will cause damage to bottom of rose leaves and can attack a variety of trees like apple, dogwood, elm, maple, oak and poplar during the summer. But it will only overwinter on rose canes. So I will be removing all canes this winter to try to break the cycle. More Info
The rose slug, Endelomyia aethiops, is a leaf eating larvae of the sawfly. These guys are tiny buggers that create a yellow and green mottled look on my rose leaves. On closer inspection, the leaves are skeletonized, with all leaf underside eaten. I have removed the worst of the leaves and may try to hose the rose this evening. See also or bristly rose slug, Cladius difformis.
With the 100 degree heat around here you cannot use a horticultural oil. I will monitor this one rose and as it cools down this weekend will apply a horticultural oil to this plant.
More info on these buggers.
Today I also found this guy on a rose bud. I am still working to determermine its identity. I moved it off this rose and to a more conspicuous area where hopefully a nice little bird will pick up for its babies’ afternoon meal! I have an email out to my local extension office. More to come.