Posted on May 09, 2006 at 16:09:23:

Question:
My grandmother has a rose bush which was fine for years and all of a sudden theres a bunch of white powder substance on the leaves and on the the roses they dont even open all the way anymore my grandma has tried everything but its still there and she dosent know what its from was hoping you would know .

Answer:
It sounds like powdery mildew to me. As with most funguses, they need to be prevented so early applications when the new growth gets two inches long and then every ten days to two weeks all through the season. If it is already on the plants, then probably a curative dose is nessesary. Fertiliome liquid fungicide works well and will last through rain.