The first line of defense in organic gardening is prevention. Choose plants that are well suited for your climate so they will be robust. If a plant and its growing environment are healthy, pest and disease problems will be minimal. There will be the right number of beneficial insects and pests to balance each other out. Use organic amendments for rich nutritious soil. Care and nurture your plants from the time of germination. Only use other means to control pests when necessary.
In organic gardening you will use a number of methods to control pests. Insect pests are often the mode of transfer for viruses and diseases. So controlling them will reduce secondary pest issues. A barrier of strong smelling herbs and flowers will deter some pests from hanging around. Examples are marigold, lavender, rosemary, oregano, chives, garlic and mint. Perennial herbs will also make a nice hedge around the vegetable garden. This will also ward off grazing rodents and deer. Herbs will attract beneficial pollinators such as bees, butterflies and hummingbirds. And they will provide culinary flavorings to use in the kitchen. All of these methods lead to a healthy garden environment.
Some pests are large and easy to see. They can be removed by hand. Slugs come out in the evening and can be dropped into a bucket of water, or salted depending on your tolerance level. Brown slugs are not native to America; the green banana slugs are. Know about the pest you are targeting, and be sure it is the culprit. Native insects have checks and balances, but alien species may not, and can get out of hand. Slugs hide under boards and rocks during the day, so you can often find them this way. Using a line of organic diatomaceous earth (fossilized diatoms) or wood ashes around the garden will keep slugs from entering the area. Small insects such as aphids can be blasted with a hose or removed with a cotton swab or cloth.
Adding the right beneficial insects to balance out the bad bugs is another organic practice. Most are safe and will not cause harm to the garden environment. These include praying mantis, soldier bug, lacewings, lady bug and beneficial wasps and nematodes. Purchase them at a garden center. They do not generally stick around from year to year, so you will need to introduce them each year. The best way to benefit from these insects is to know their target insect, and release them when it is active.
Bacillus thuringiensis or (BT) is a bacterium that will kill certain insects. It causes digestive issues and the insect stops eating and dies over a period of days. There are many different types that target different insects. Because this bacteria can also target beneficial insects like butterflies, it should only be used by knowledgeable gardeners, and when the imposing insect is rampant. it does not otherwise harm the environment as a whole. BT is usually applied as a dusting of white power containing the bacteria. Pheromones (insect mating hormones) are also taken from insects and used to attract pests to traps. These traps are hung in trees that are under attack by the insects. Biological controls are applied during a certain part of an insect's life cycle. Some understanding of entomology is helpful when using these tools.
There are times when all other means have been employed, and bugs get out of control. The first approach is to discourage insects. Applying organic insecticidal soap as well as sprays made with hot peppers or garlic will send sucking and biting insects away. For those more tenacious insects, try natural horticultural oils. Neem is the leading choice for safe and effective insect control. Since a pest can also be a carrier of viruses or fungi, neem also chokes out these pests. It must be applied when temperatures are 60 degrees F or more. It also must be reapplied after a heavy rain. Organic sprays can cause leaf burn if applied in the hot afternoon sun. There are also plant-based pesticides such as pyrethrin, sabadilla and rotenone. These are botanical based insecticides. They may be natural but they are not selective and will kill good and bad insects. This is important to note since beneficial insects will help bring balance back to the garden. Extreme means of control are only temporary and can leave the garden undefended. Use them only as a last resort. What is even better is to plant something else less desirable to the insects in question.