There are a few varieties of apple available that are resistant to apple scab and cedar apple rust. These resistant varieties will not require fungicide sprays.  They are not resistant to insect pests so insecticides may be needed.  The quality of the fruit from these disease resistant trees is acceptable, although it may not measure up to that of some other varieties. 

 ‘William’s Pride’ is resistant to apple scab.

Cedar apple rust resistant cultivars include ‘Fireside’, ‘Freedom’,  ‘Nova’, ‘Easygro’, and Novamac’

‘Liberty’ and ‘Redfree’ are both scab and rust resistant.

Life expectancy for a dwarf tree is somewhat determined by the type of rootstock used.  In general, a dwarf apple may live 15-20 years.  A semi-dwarf tree may see 20 – 25 years while a full sized tree should manage 35 to 45 years.  Those are just general guides and there are certainly many trees that don’t fall within those parameters.

Faye 
Thank you.
Rootstock would help explain the short lifespan of my Fireside. Cut down my Jonathan - a total loss. Very susceptible to rust:never a problem in the UK.
I find that the plastic bag method -- cut holes in the lower two corners -- works well to keep the apple maggots off my Haral Red. I use sandwich (not fold over).Prior to that had not had an edible apple for years. May try paper bags next year since the plastic does cause some problems, having found bitter rot on a few and plastic does help the scab. Didn't check microscopically but used to work with Colletotrichum.  Incidentally one Master Gardener told me to use the bags and another positively told me off. But it does work to keep maggots and moths off and the texture is good. Just time consuming.

Stephanie, I am glad my answer gave you something useful.  And on behalf of all the MN master gardeners, I apologize for your bad experience with one.  I assure you that it isn't what we strive to do.  
 The paper bags sound like an excellent idea.
 Best of luck!

Just for your information, the Master Gardener who told me off about using plastic bags had tried them and "the apples were mushy". She cut down her tree(s). I suspect she did not cut the corners off and partly cooked the apples.