Know how long the pesticide remains effective on the plant. This is also important in food crops. You must observe the prescribed time lapse between the last application and harvest. You may want to apply a pesticide and then enclose the plants in netting to keep further infestation from occurring. Or, you may decide to put up netting and then release predators.
Diseases are more difficult to control.
Most of the fungicides prevent infection or at best stop an infection from spreading. Apply controls as instructed. Netting is not effective if there are unprotected areas. Pesticides must be applied to both the top and underside of leaves. Application rates are critical.