Your plantings should not be fertilized between the end of July and the middle of October. The healthier your plants are the less they will be affected by an insect infestation or a plant disease. To keep your plants as healthy as possible you need to reduce the stress that would normally weaken a plant. This can be done by providing proper watering, mulching and fertilizing. Inspecting your plants periodically will keep you on top of any problems that might develop.
Most insect problems are quite visible and fairly easy to control.
Insecticidal soap, for example, will control a majority of the common insects with minimal environmental or personal hazard. Disease problems are more difficult to diagnose. These problems should probably be referred to your county horticultural agent or university extension people, who have the appropriate testing facilities. Because of the nature of their jobs, they are often aware of any regional or area disease problems and can suggest proper treatment. Your McKay Representative can recommend someone for you to contact, and possibly make recommendations, particularly for more common problems.