More than 2000 types of apples are grown in the United States with over 7,000 types worldwide. With those numbers, it is little wonder when problems are encountered. Between insect pests, viruses and even a fungus named after them, apples can suffer from numerous afflictions. With apples being such an important food crop, knowing what can adversely affect them is important to ensure their growing success.
Cedar-apple rust is a fungus that is spread from cedar trees to apples. The spores of this fungus are held in galls throughout the branches of cedar trees. When exposed to moisture in the spring, they produce bright orange, gelatinous "fingers" appearing like frilly Christmas ornaments on the tree. Symptoms on apple trees include leaf lesions and discoloration of leaves and fruit, often appearing to have a splotchy, rusty appearance.
Treatment and prevention for cedar apple rust is by use of fungicides, removing affected cedars or, in the case of some, destroying all cedar trees within the growing area. The apple variety "delicious" has a natural resistance to cedar-apple rust.
Insects can create havoc in the home orchard. Coddling moths are well known to apple and pear growers for the damage they inflict on their crops. Destructive coddling moth larvae tunnel through fruit, leaving unsightly holes as they feed before locating a dark, safe place to pupate.
Carbaryl (Sevin) and permethrin are common treatments for preventing coddling moth infestations. Yellow sticky traps and red apple shaped sticky traps are used to catch apple maggot flies before they have a chance to endanger crops.
High temperatures in correlation with strong light can cause apple fruit to take on an unsightly burned appearance. You can avoid this problem by slowly exposing fruit to the sun instead of instant, drastic pruning, or by shading fruit until it has acclimated to the sun. Lighter skinned apples are prone to burning while the darker skinned types are less likely to develop this issue. Symptoms include light-colored discolorations on fruit that can later darken to brown. There is no treatment for sunburned apples.