Hi, 

It is from Roseslug Sawflies which commonly effect roses. You can send photos of the entire shrub which may be helping. The leaf photo isn't showing what the white is clearly enough but it is probably some shed skin of an insect that isn't harmful. You can review our diagnostic page for roses and the tab for Roseslug Sawflies. You can hand pick off any of the small green worm like caterpillars or you can try using a contact insecticide like insecticidal soap or horticultural oil but be sure to read the label directions- hort. oil can burn the foliage in high temperatures. Since these are contact insecticides they need to be sprayed directly on the pests, so try to get underneath the leaves as well -the likely area that the larva are. Also just be cautious with spraying pollinators in the process. 

Most roses even in heavy infestations and leaf drop will re-leaf out again and be fine. 

Let us know if you have further questions. 

Emily