Aphids
These small insects appear in cooler seasons of the year and suck out the juices of the leaves.  Curled leaves are a common sign of their presence. 

Lady bugs can be effective in their control. Since ants live off the secretions of aphids, it is helpful to wrap Tree Tanglefoot (see Orchard and Garden Supplies in our online catalog) around the trunks to prevent ants from crawling upward.  Other remedies include insecticidal soap spray and horticultural oil spray in the dormant season to kill over-wintering eggs.

Scab
The leaves show dark blotches and the fruit has scabs. Dormant sprays such as copper and lime sulfur applied in the winter and early spring are good preventatives. More about Apple Scab...

Coddling Moths
The moths lay their eggs in early spring on the open apple blossoms. The larvae then develop inside the apple and eat their way out. 

Traps containing a pheromone should be hung in the trees as soon as the blossoms appear. They serve as an indicator and, in cases where the moth population is small, may be a satisfactory deterrent.  Check with your local nursery for an appropriate insecticide should you need to spray. Be sure to dispose of all the old fruit from the previous year.

Fire Blight
This is a bacterial disease common to apples, pears and other related plants. The leaves turn brown, then black, giving the appearance of having been scorched. Prune the infected area back, being sure to disinfect the pruning implement with alcohol after use.

Common household bleach sprayed in the immediate vicinity of the infection may be helpful. Copper sprays may be applied when the trees are dormant.