Sometimes, in spite of our best efforts, things go wrong. The culprits are weeds, pests, diseases, or environmental problems like not enough light or too much water. Your first line of defense is healthy plants. Garden plants evolved in the wild along with the insects and disease organisms that plague them, so they have developed defenses against these pests. Most of the defenses are chemical. Many of the compounds that give plants their flavor or character are created by the plant as a defense against some sort of pest. The aromatic compounds for which we value herbs, for example, are natural insecticides. The sulfur compounds that give radishes and mustard greens their pungency repel insects.
Strong plants are more able to make these compounds than weak plants. For this reason, vegetables that are well established and healthy fight off pests and diseases better than weak or sick plants. This is so true that many pests recognize weak plants and are drawn to them, just as a wolf will pick the weakest caribou in the herd to attack.
After keeping your plants healthy, the best way to prevent pest and disease problems is to select varieties that are naturally resistant to them. Most herbs, for example, grow with little or no attention on your part and are seldom bothered by pests or diseases. Also, some vegetable varieties have been bred to have natural resistance to specific problems. Some corn cultivars, for example, have ears that are so tightly wrapped in the husk that corn earworms can’t penetrate them. Some tomato varieties are resistant to a range of diseases.
If you know that a particular pest is an ongoing and serious problem in your area, either search for resistant varieties or don’t grow that vegetable at all. For example, if asparagus beetles attack your asparagus every year and you are tired of fighting them, pull out your asparagus and buy it from the store. Plant strawberries or rhubarb instead.
But if You Can’t Avoid it
But problems arise in the best-cared-for gardens. Insects are best controlled by vigilance. Watch for signs of insect problems and nip them in the bud as soon as they appear. A few aphids are much easier to deal with than thousands of them.
Vegetable diseases can sometimes be controlled with fungicides, or by correcting environmental conditions that favor the disease.
Half-eaten leaves and slimy, silver trails on the earth are signs that you have one of the worst of all garden pests. Snails and slugs abound in lush, closely planted vegetables and are especially difficult to control in cool, damp climates. If you do not get rid of them, you will quickly have a population explosion. Bait containing metaldehyde is very effective. Snail killer is safe to use around vegetables. See Controlling Slugs and Snails in Vegetables for more information.
Like insects, weeds are best controlled with vigilance. Create conditions that favor the vegetables and repress weeds, then be vigilant for interlopers and get rid of them before they set seed. See Controlling Weeds in Vegetable Gardens for information.