Properly fertilized, watered and weeded, the prolific tomato plant is capable of producing a bumper crop of succulent fruit---for people and for a variety of tomato plant pests in the form of hungry insects. Whether they're in search of the rich, green foliage or the tomato plant's luscious, red fruit, chances are you've run into at least one of these pests if you've ever grown tomatoes. The key to keeping tomato plant pests out of your garden is to know them--and common signs of their presence--by sight.
Pick the insect off your tomato plant and put it in a bucket to keep it contained while you identify it. Wear rubber gloves to pick the insect up, since some garden pests such as the blister beetle actually secrete toxins that can irritate your bare skin. Before you remove the insect, note what area of your garden the insect came from. Was it on a ripe tomato or munching on the tomato's green foliage? Was it on the soil beneath the tomato? Considering questions such as these can help you determine if the insect is a friend or foe.
Insects that are actually on your tomato plant are almost always pests, especially if they're in groups. If the insect was on the ground by a tomato plant and it's by itself, it could easily be harmless to your tomatoes.
Identify the main physical characteristics of the insect that you've captured. Observe the body shape, length, color patterns and any other distinguishing characteristics. If you found a beetle, look for an elongated oval shape and black and yellow stripes, which could indicate blister beetles, potato beetles or flea beetles, which are all tomato plant pests.
Similarly, many tomato pests are moths in the larval stage of development, so they'll look like worms or caterpillars; examples of these include the tomato hornworm and the tomato fruitworm. Use the information you gather about the insect together with your assessment of the plant damage to determine if the insect is a tomato plant pest.
Look for chew marks on your tomato plant leaves. Holes and chew marks in the leaves may indicate the presence of a range of tomato plant pests, including the blister beetle, the hornworm, the cabbage looper, the potato beetle and flea beetles. The size of the holes often indicates the pest that's causing the damage. For instance, according to the North Carolina State University Cooperative Extension, flea beetles create tiny holes, whereas the hornworm may actually strip entire leaves from the tomato plant vines.
Check your tomato plant leaves for leaf discoloration and deformities, including the undersides of the leaves. Deformities include leaves with abnormal shapes, leaves that curl as they grow and leaves that are stunted or show little growth. This sort of plant damage occurs as a result of tomato pests that suck the sap out of your tomatoes, resulting in a weak, damaged plant. Sap-sucking insect pests include aphids, whiteflies and stinkbugs.
Look for damage on your tomato fruit and the buds, including holes and blotched or scarred areas. This type of damage almost always indicates the presence of a tomato plant pest. Tomato pests that often affect this part of your plant include worms such as the tomato pinworm, the tobacco budworm and the tomato fruitworm.
Investigate damage on the roots and stems of your tomato plants. Look for holes in the plant at the base of the stem, as well as burrowing holes in the soil right around the stem. Tomato pests that consume this area of your plant include the cutworm and the wireworm.