Flesh color also loses its greenish tint and turns yellow or white. A mature fruit will be crisp and juicy. A pleasing taste is the final indicator of fruit maturity. Apple trees sometimes fail to produce fruits for many reasons. Some of these reasons include lack of time to reach bearing age, lack of compatible pollinating cultivars, absence of honeybees or bumblebees, attack by insects and diseases, too much shading, unfavorable weather, improper pruning, too much nitrogen application, and the tendency of some cultivars to produce heavy for one year and light for the following.
Apples have many diseases and insect pests.
Some of the common diseases that attack apple trees are apple scab, powdery mildew, black rot and frogeye leaf spot, rusts, collar rot, sooty blotch and fly speck, and fire blight. Some of the common insects and mites attacking apples are apple maggot, codling moth, plum curculio, San Jose Scale, European red mite, and aphids. Apple cultivars listed in Table 1 are not resistant to insects or mites. Ohio Commercial Tree Fruit Spray Guide, for more information on disease and insect management. Useful References 1.