The last thing you want to see in your vegetable garden are chunks taken out of leaves and wilting plants. In many cases, the culprits are among the many species of insects that feed on vegetation, damaging or killing plants in the process. Keeping them away from your garden is as much about prevention as it is about eliminating the bugs once the damage has been done, and there are steps you can take long before a single plant germinates to minimize their impact on your vegetables.
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The condition of your garden soil can provide the first line of defense against marauding bugs. Sterilize the soil about six months before the next growing season by covering it with black plastic mulch. The heat generated below the plastic effectively kills insects at all stages of development, along with weed seeds and roots. When you're ready to till the garden, remove the plastic and aerate the soil by loosening it with a hoe or garden fork to bring any remaining pests to the surface by disrupting their habitat. Work plenty of organic matter, such as aged manure or compost, into the soil at this point to promote microbial activity that also eliminates many harmful bugs. If you're working with soil that hasn't been solarized, be sure to remove all traces of old decaying vegetation that can harbor bugs.
On planting day, examine all seedlings, and discard any that show signs of insect infestation or damage. The Purdue University Extension website recommends planting at the right time, as slow growth in soil that is still too cool or wet leaves plants vulnerable to certain types of soil-borne bugs. Maximize air circulation between plants by following the minimum spacing guidelines when planting both seedlings and seeds. Correct spacing also allows the soil to dry and discourages insect colonization by preventing them from moving easily from one plant to the other. Water the vegetable plants at soil level early in the day, and avoid splashing the leaves, as wet foliage is more susceptible to insect damage.
In general, the sturdier and healthier a vegetable plant is, the more resistant it will be to bugs. Keep the vegetable garden well-weeded, and remove any plants that show signs of distress. Harvest all vegetables promptly to prevent the spread of decay and disease created by insects. While a serious bug infestation calls for more aggressive measures, many insects, such as aphids, thrips and spider mites can be controlled with a solution of 1 teaspoon neem oil, 1/4 teaspoon insecticidal or dish soap and 1 quart of water. Spray all parts of the plants at the first sign of trouble, and every week as needed. Do not spray when temperatures are above 90 degrees Fahrenheit or when conditions are sunny, or damage to foliage can occur.
If your bug problem is severe enough to warrant the use of chemical pesticides, do your homework before hitting the spray nozzle. The effective use of pesticides depends entirely upon knowing exactly what species of bug is eating your veggies, and there is no general-purpose formula that kills them all. Some pesticides work only on the bug's larvae, while others attack juvenile or adult bugs only, so it's important to know what you're dealing with. You can get help with this through your local county extension office or at a reputable garden center, as some pesticides may kill not only the offending bug but other beneficial ones as well.
Choose pesticides intended for edible crops wisely, and start with substances that pose the lowest risk of contamination. Ready-to-use insecticidal soaps, horticultural oils and biological controls such as Bacillus thuringiensis (BT), a bacterium that works against certain destructive insects, are generally safer to use than chemical pesticides. Spray all portions of the affected foliage and repeat weekly, if needed. To prevent damage to the plant, do not use these products when temperatures are above 90 degrees Fahrenheit or while conditions are sunny. Read labels carefully, follow instructions and precautions to the letter, and wait the recommended time before harvesting vegetables after using insecticides. As an added precaution, wash all your produce thoroughly before eating or cooking.