There are many ways to ward off pests in the garden. Spraying a vegetable crop with an approved, biologically friendly insecticide is one option, but generally that method is considered a last resort. Sometimes an insecticidal soap will do the job. Often, an application of a natural remedy specific to the pest is more effective.
The most reliable method of dealing with pests in the vegetable garden is to scout for pests on a weekly basis and to deal with any potential problems through more garden-friendly means, such as hand-picking pests off plants before they balloon into real trouble. Preemptive measures, such as row covers, provide a physical barrier to prevent pests from reaching their target. There are other, reliable, preventative techniques; for instance, cutworms may be kept away from tomato plants by wrapping a small piece of a glossy magazine cover around the plant’s base; the cutworm will not gnaw through this protective shield.
Dealing with the appearance of cabbage worm in your vegetable garden is a good example of using a natural approach. In May, you might see pretty little white butterflies hovering around your cabbages and shortly thereafter you will notice some holes appearing in your leaves until the beautiful, glaucous foliage is covered with perforations. You have cabbage worms. The easiest way to control this problem is to handpick the small green caterpillars. Sometimes spraying the plants with insecticidal soap or hot pepper sauce helps but it is more effective to spray all cole crops (Brassica) with BT (Bacillus thuringiensis), soil-dwelling bacteria that are harmless to humans but devastating to caterpillars, and to order some insect netting to make covers for your cabbages.
Companion planting is a traditional practice for warding off pests. Plants with strong fragrances confuse many pests and prevent them from finding target crops. The classics are marigolds (Tagetes) and scented geraniums (Pelargonium). A favorite marigold for this purpose is the signet marigold (Tagetes tenuifolia) with its sweet lemony fragrance. While the odor of many marigolds deters pests, it is also overwhelming for the gardener. The ‘Gem Series’ has an inviting fragrance. A favorite scented geranium is the peppermint geranium (Pelargonium tomentosum) with its velvety leaves.
Similar to companion planting is the notion of trap crops. Instead of warding off potential pests, trap crops entice the pests and either destroy them or act as a sacrificial lamb and bear the brunt of the pests’ destruction. An example of this is the planting of four-o’ clocks (Mirabilis), scented geraniums (Pelargonium), or larkspur (Consolida) near roses. The trap crops purportedly act as decoys, attracting rose-loving Japanese beetles to eat their poisonous leaves.
In the commercial trade, vegetable growers often use the method of perimeter trap cropping as a means of protection. It is like building a fortress wall around the field as the trap crops either kill the pest or retain it within the border so that it doesn’t stray to the main crop. Growers often surround their cabbages (Brassica oleracea capitata group) with collards (Brassica oleracea) to protect the cabbages from attack of a particular moth. If the population gets too large, then farmers introduce a parasitic wasp (a beneficial insect that preys on the pest) as additional help to prevent the moth from journeying to the cabbage. Similarly, to prevent pepper maggot infestation, cherry peppers (Capsicum annuum) are used to surround bell peppers (Capsicum annuum). Cucumber beetles and squash vine borers are kept away from yellow summer squash (Curcurbita pepo) by border of Blue Hubbard squash (Curcurbita maxima).
Many insects don’t like to land on soil and will look for something nice and green to use as a landing strip. Tests have shown that if you plant clover (Trifolium, a good cover crop) around cabbage then cabbage root flies will have a difficult time finding the right space to lay their eggs. They will land on the clover, realize they are on the wrong plant, try again, and then finally get discouraged by not reaching their goal.
If your pests are four-legged (cats, rabbits, squirrels), repelling with scent can be effective. Cats hate the smell of citrus; try placing orange peel on top of the soil. Spray plant leaves with a homemade blend of water, a few drops of Tabasco sauce and a sprinkle of cayenne pepper or with a commercial hot pepper sauce. In some cases, you can place gravel or pebbles as a mulch around your plants to stop animals from digging in the soil.
What is always true is that good horticultural practices are the essential backbone to a healthy vegetable garden. They will not do anything to eradicate pests, but they will help support the plant while it is trying to defend itself from an attack. Amend your soil with compost or dehydrated manure in the spring. Soil preparation is important for several reason. Plants need water, nutrients and oxygen to grow. When you turn the soil and amend it with compost, you are aerating it, improving soil structure and friability, and thereby increasing its capacity to hold water. Healthy soil amended with compost makes for healthier plants that are not only prolific by also more disease-resistant. Fertilizers such as fish emulsions and seaweed, which are popular in the vegetable world, are vitamin pills for plants, a nice boost but not the main meal. Keep vegetables well-watered in summer and mulch your vegetable beds once they are planted and the soil has warmed up to help retain moisture. Finally, if there is a serious pest problem on anything in your garden, it is better to address it sooner rather than later.
Attracting Beneficial Bugs to Your Garden by 
The Organic Gardener's Handbook of Natural Pest and Disease Control by 
The Vegetable Gardener's Bible by 
What's Wrong with My Vegetable Garden? by 
