Preventive fungicide sprays are the only ones worth doing. You only need to do that when the weather conditions are favorable for fungal growth. Cultural control like making sure you have adequate spacing, good sanitation, and good air circulation is the best prevention as is making your plants as healthy as they can be.
You should identify your pest before you start and insect spray program, especially on things you are planning to eat.
Soaps and oils are contact sprays and don't work on hard bodied pests like beetles and must make contact with the pest to work. If there are no pests to spray or you are not spraying where they are and getting good contact it is a waste of time and money.
Be careful with horticultural oils and sulfur, they cannot be used within two weeks of each other and if the days are over 80 degrees, they can burn plants.
Plant to attract beneficial insects and provide habitat for them. Natural predators and healthy plants are really the best controls. AACT is good for plants. I find that the plants are not bigger, but they are healthier with its use.
When it is hot and dry put out a shallow tray filled with river pebbles and water. This is the only use I have for a pot saucer. It provides water for bees, butterflies and other pollinators and beneficial insects. The other way to do that is to water the garden early in the morning and the insects will lap up the water off the leaves and petals.
Not using pesticides unless you absolutely have to, will preserve the natural predators. You need to establish a threshold to determine when you treat. Hand picking is really the only selective option.
As plants get older they become weaker and more susceptible to disease and insects will always go after the weakest plants. Knowing when a plant is nearing its useful life is important. Pulling the sick plants is sometimes better than trying to treat them. Scout the plants daily, look for and recognize the pest and disease problems. Treat them before they so weaken the plant, that there really is nothing left to save.
On the other hand, some damage is tolerable. Unless you are growing ornamental plants, I don't bother with a few leaf miners.
https://www.farmerfred.com/plants_that_a ... enefi.html
Happy gardening in Hawaii. Gardens are where people grow.