Tomato plants are susceptible to a number of diseases and pests, most of which can be treated with insecticidal or fungicidal sprays. If you plant to eat your tomatoes, only apply organic and food-safe sprays. Otherwise, you may render your tomato plants inedible and poison the water supply. If you find that organic sprays are ineffective or that the disease or infestation persists from season to season, switch to a variety of tomato plant that is resistant to the disease or pest that is afflicting your garden.
Identify the pest or disease afflicting your tomato plants. Common tomato pests are beetles, aphids, worms, slugs and cabbage loopers. Common tomato diseases include blight fungus, leaf spot, anthracnose, and bacterial speck. Examine your tomato plants leaves, stems and fruit for pests or the tell tale signs of specific insects, bacteria or fungus. When in doubt, take a sample of the damage or insect into your local garden center.
Removed any insects or diseased foliage. Use a pair of clean pruning shears to remove material from the plant (take care to disinfect them afterward). Large insects can be picked off by a gloved hand and dropped into a bucket of soapy water. Also remove any litter from the base of the plant. It is likely harboring insects, fungal spores or bacteria.
Wait for ideal conditions to spray. Only apply spray when there is little to no wind and no rain forecast for the next few days. Apply spray early in the morning or late in the evening.
Cover any plants that you do not intend to spray with a plastic sheet.
Mix the concentrate spray with water according to the manufacturer's instructions (if applicable). Do not increase the strength of the solution in an attempt to make it more affective. This may harm the tomato plant.
Spray the plant according to the manufacturer's instructions. Be sure to spray the underside of the leaves, and focus on any area where you have seen insect activity. Coat the plant, but stop before the spray is dripping off the plant.
Monitor your plants and re-spray them as needed (no sooner than the intervals prescribed by the manufacturer).