Disease and Pests

Fireblight can kill susceptible varieties under favorable conditions.  If you have wet springs, it is advised that you only purchase blight resistant trees to keep damage to a minimal.  Apple scab will primarily harm the fruit.  Apples that are affected are still edible, but it will reduce their storage duration.  Cedar apple rust can infect the leaves, fruit, and young twigs in areas that contain junipers.  This is particularly true for the eastern red cedar (Juniperus virginiana), which is common throughout the eastern half of the United States.

Apples are quite susceptible to a number of pests.  Codling moth is the most damaging, but plum curculio can greatly disfigure them in high pressure areas.  The apple maggot fly is a fairly common issue as well.

Biennial Bearing

Some apples labeled as annual bearers may behave in a biennial manner, and many biennial apples can be annual bearers if thinned heavily early in the season.  Other factors that may determine if a variety is biennial or not includes exposure to shade, soil nutrition, and rootstock.

Storage

Apples are best stored between the temperatures of 32-38F, but some of the longest storing varieties may be able to last for awhile around temperatures as high as 55F (based on a very limited amount of experience).  Many varieties, particularly the more acidic ones, will develop a better flavor (and decrease acidity) after a month or so in storage.  Other varieties will lose flavor rather quickly.

Other

Apples aren't affected by an occasional light frost.  They can handle temperatures around 26F for some time without freezing.  High sugar apples may be apple to handle temperatures a few degrees lower.