The best dwarf apple rootstock to use is Bud 9 (Budagovsky 9). It is resistant to problems like fire blight, apple scab, powdery mildew and collar rot. Bud 9 will also help the tree to avoid frost damage.
About this Author
Marie Notnats enjoys learning about new topics and teaching people new skills. She has been writing professionally since 2008. She is a professional horticulturist with a Bachelor of Science degree in horticulture from Brigham Young University. She writes for About.com, Examiner.com, eHow, and assorted gardening blogs.