A: Depending on the insect you are trying to eradicate, various products that are designed to do the job well are readily available. For aphids and wooly aphids, I like to use the SAFER brand insecticidal soap.
For mealybug and the common brown scale, I like to use another SAFER brand product called YARD & GARDEN. In the case of the adult scale however, a horticultural oil( such as ULTRAFINE) may need to be used because the adults have a protective exoskeleton.
Whenever oils are used, a few precautions are warranted as the oil itself can sometimes cause more harm than good if not used properly. Some plant species more than others are susceptible to damage from oils. I would advise spraying the product on a few branches prior to full coverage to test for phytotoxicity. As an extra precaution, apply the oil just before sunset and rinse away the next morning using water from a hose.
If mites are your problem, consider a product from the MONTEREY brand called SAFETYCIDE or you can use common sulfur dust. The best pesticide that I have used is TREE TANGLEFOOT Pest Barrier(Available at most nurseries or Home Depot). Although not really a pesticide, the Tanglefoot works very well at removing ants from your plants thereby allowing the natural beneficial predators to do their job eating the undesirables. When used properly, the effectiveness of the Tanglefoot is undeniable.
One such example in recent memory is that of a 25′ tall ‘McDill’ white sapote tree 30% covered with a brown scale infestation. To large of a tree to spray, I simply applied a 3″ wide band of the Tanglefoot to the main trunk about two feet up from the ground. In three weeks time almost all the scale were dead because they were parasitized by a tiny predatory wasp thereby solving the problem naturally! Remember to look out for any ant(Argentine ant) trails leading to your fruit trees as that is almost always a guarantee that there are some other undesirable insects on that tree causing damage.