Growing tomatoes is a rewarding experience, and one that would be more pleasurable if tomatoes weren’t so darn attractive to pests. Dealing with insect pests is my least favorite task in the vegetable garden, but I try to stay ahead of potential outbreaks by inspecting plants early and often. The four pests highlighted here — hornworms, leaf-footed bugs, aphids and spider mites — are significant challenges for tomato gardeners, but with proper identification and early detection, steps can be taken to minimize damage to plants and fruit without resorting to insecticides that may harm beneficial visitors in our gardens.
Hornworms. This doozy of a caterpillar, actually the larva of the hawk or sphinx moth, is best dealt with before it develops the ravenous appetite that can absolutely strip a young plant of its leaves. Hornworms can be extremely destructive to tomato plants, especially if these pests go unnoticed — a likely occurrence due to their crafty ability to blend with a plant. Even though they are masters at camouflage, they can’t hide their telltale excrement that looks like miniature hand grenades. If you see pellets on the ground or on a leaf, look up and you will likely find the culprit, either a tomato hornworm or a tobacco hornworm munching away.
Similar in size, appearance and appetite, these two tomato-plant defoliators are distinguished by their markings. A tomato hornworm has white V-shaped stripes on its body and a black horn on its tail end. The tobacco hornworm has white diagonal stripes along its body with a red-tipped horn at its end. Because these caterpillars generally show up in small numbers, one or maybe two, the easiest solution is to handpick and discard the caterpillar or toss it to birds or chickens.
Leaf-footed bugs. Leaf-footed bugs are a nuisance because they use their long tubular proboscis to pierce plant tissue. They suck out the juices and cause unsightly blemishes on prized tomatoes. And though this poke-and-suck feeding habit causes no harm to humans who consume damaged fruit, it sure detracts from the enjoyment of a homegrown, vine-ripened tomato. Puncture wounds also provide an entry point for pathogens, which may cause fruit to rot.
Inspect tomato plants, as well as surrounding weeds and landscape plants, often during tomato season, as leaf-footed bugs are much easier to control early in their life cycle — and I mean early, starting at the egg stage. Eggs are laid in a strand along stems or the underside of leaves and are easy to crush, unless, like me, you are curious to watch them hatch. Once they do hatch, the orange and black nymphs aggregate in clusters and their soft bodies are easy to squish or brush into a bucket of soapy water. A light-colored sheet or layer of newspaper on the ground makes it easy to collect escapees. At this immature stage, they do not have wings to fly away, emit no odor when crushed and are more vulnerable when sprayed with insecticidal soap.
Adults, on the other hand, are armored with wings and a protective exoskeleton that make them a more challenging foe. Gardeners go to great lengths to protect their tomatoes from these exasperating pests. Some of the more effective methods I’ve seen include growing tomatoes inside a tent or large cage covered with nylon netting, using a small hand vacuum to suck the bugs off plants and wrapping individual tomatoes in small mesh bags (tulle party-favor bags purchased from Amazon).
Another useful technique is growing a trap crop. Leaf-footed bugs love tomatoes, but they seem to love sunflowers, cardoon and artichoke plants even more. These are examples of trap crops that can be planted near the garden to divert leaf-footed bugs away from tomato plants. Once they begin to congregate on the trap crop, they can be handpicked, sprayed, squished or otherwise eliminated. Sometimes trap crops are considered sacrificial plants that can be wrapped, pulled up and discarded once they are heavily infested with target pests.
Aphids. One aphid is no big deal, but colonies of aphids can damage foliage. These pests, also known as plant lice, suck the juices from leaves, causing yellowing, wilting and loss of plant vigor. In the process, they produce sticky honeydew secretions that can attract fire ants. If that’s not bad enough, they are also vectors of disease. Their damage can escalate quickly because they multiply rapidly and can produce several generations, mostly females, during tomato season. These small insects can come in shades of green, yellow or gray, and they have two distinctive tailpipes, called cornicles, protruding from the posterior end of the abdomen.
Aphids favor new tender growth and tend to congregate near the tips of new shoots and on the underside of leaves, where they are protected from sun and wind. The good news is that they have soft bodies and most of them do not have wings. So, they are easy to scrape from a leaf, smother with insecticidal soap or dislodge with a strong spray of water. You won’t get them all the first time, so spray at intervals to nab stragglers and subsequent generations. Tender, tasty aphids are a favorite snack of lady beetles and their larvae, and they will devour them by the hundreds if we don’t interfere. Remember, most insects in a vegetable garden are beneficial or neutral, so be judicious when applying any kind of pesticide. There’s no need to smother every single plant with dusts or sprays; even organic products can kill the good guys.
Spider mites. Tiny yet mighty, these rapidly reproducing relatives of spiders and ticks can be highly destructive if their numbers explode. Though hard to see without a hand lens, they are generally found on the underside of leaves, where they puncture plant cells and suck the contents, causing a light-colored stippled effect on the surface. If the population grows unchecked, these spots grow, creating larger sections of yellowing until the leaf succumbs and turns dry and tan-hued. In severe infestations, mites form a ghastly webbing around sections of leaves. But let’s not allow that happen to our tomatoes!
Spider mites, like aphids, can be dislodged with a strong spray of water. They also like hot, dry conditions; so regular sprays of water (at least one-to-two times per week) will disrupt this environment and discourage their growth. For persistent infestations, insecticidal soap (a low-impact contact insecticide) may provide effective control. Follow label instructions and note that multiple applications may be necessary, as mites will likely hatch from eggs that withstand the initial treatment.
By Patty G. Leander, B.S.
Contributing Editor
Advanced Master Gardener — Vegetables