Answer: Apples are subject to any number of foliar problems due to both insect and disease, and some varieties are more susceptible than others. Most home orchardists find it necessary to follow a routine preventive spray program of some sort in order to keep their trees healthy. The potential problems depend on the built-in susceptibilities and resistances of the varieties you grow, the prevalence of certain problems in your local area, and the weather each year. The timing for the treatment(s) is usually critical and may begin in mid winter for certain diseases and pests. I would suggest you contact your local county extension (349-1247) for a specific diagnosis and steps to take now (if any) and the suggested routine for the varieties you have on your tree. In the meantime, be sure to clean up and remove and destroy any fallen leaves, twigs or fruit both during the season and this fall to try to limit reinfection.
In general, fertilizing would be done based on the results of soil tests, and once basic nutritional needs are met additional ferilizing is not helpful and may further stress the tree. Your county extension can also help with the soil tests and interpreting the results. The best thing you can do for the tree is to make sure it is kept watered while it becomes established. Try to provide a deep watering about once a week or as needed to keep the soil moist but not soggy along with an area of several inches of organic mulch under the drip line -- but not touching the trunk.
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