Tomato Insect Pest Management

A very large green, striped caterpillar with a pointy horn-like appendage

Tomato hornworms can defoliate a plant in a matter of days. Credit: Whitney Cranshaw, Colorado State University, Bugwood.org

Tomatoes are a staple in gardens across the county. In Florida, however, year-round high temperatures present a unique problem: year-round pests.

Below are a number of Florida's most common tomato insect pests. No garden will ever be pest free, but with integrated pest management, or IPM, you can enjoy your harvest and still protect the pollinators that service your garden.

IPM is a comprehensive approach to managing plant pests. The goal is to cause the least harm to people, property, and the environment. Before you reach for a chemical solution, consider learning more about integrated pest management.

Tomato Hornworm

Damage caused by the larva of a tomato hornworm. Credit: UF/IFAS Plant Pathology

Tomato hornworms (Manduca quinquemaculata) are one of the most dramatic pests a gardener encounters. They are bright green, striped, up to three inches long, and sport a thick horn on their rear. In northern Florida this species can go through 3-4 generations each year, and our tomatoes are one of their host plants. A single hornworm larva can strip a tomato plant bare in a matter of days. They have been known to feed on green, immature fruit as well. After the larva is well fed, it pupates and undergoes metamorphosis. It emerges an adult: a large, thick-bodied moth. These adults are nocturnal, so you aren't likely to see them on a garden walkthrough.

Multiple IPM techniques are effective in controlling hornworms. Cultural management uses the way you garden to keep pests at bay. Handpicking and destroying the larvae is one popular method of cultural management. A second cultural management practice is also effective: because hornworms pupate in the top few inches of soil, tilling between crops results in 90% mortality to the pupae.

Hornworms occasionally attack immature fruits as well. Credit: UF/IFAS Plant Pathology

To control tomato hornworms, and other caterpillars, IPM biological controls are also effective. Bacillus thuringiensis, also referred to as Bt, is a species of bacteria. When ingested, it is toxic to the larvae of Lepidopterans (moths and butterflies). The key to using Bt as an insect control is to apply it routinely. It is most effective if it is present when the larvae first hatch. Best of all, Bt won't harm beneficial insects!

Attracting beneficial insects (and keeping them alive) is another form of biological control, and very helpful in controlling pests. Hornworms are preyed upon by several native parasitic wasps. If wasps frequent your garden, cheer them on and leave them to their work.


Tomato Fruitworm

A tomato fruitworm, living up to its common name. Credit: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Tomato fruitworm (Heliocoverpa zea) causes damage in its larval stage. After feeding on tomato fruits, it pupates into a large moth, about 1.5 inches in wingspan. Adults deposit their eggs one at a time, each on the underside of its own leaf. The egg hatches within a few days and for 2-3 weeks the larvae feasts on your tomato plants. While they do sometimes feed on leaves, this pest primarily damages the fruits. They chew deep holes into ripening tomatoes, usually from the stem end.

As with tomato hornworms, handpicking and Bt are highly effective. Apply Bt early and often to control the larvae while they are young. The bacterium is less affective at controlling mature caterpillars. Parasitic wasps and cultural control are also effective in managing fruitworms.


Whiteflies and Aphids

Whiteflies and aphids are small, but mighty. While they are not closely related, they do cause similar types of damage and respond to similar methods of control. Adult whitefly females lay their eggs on young leaves.

Leaf damage caused by sap-sucking pests. Credit: UF/IFAS Plant Pathology

From there, the eggs hatch and can mature into adults in as little as two weeks. Immature whiteflies (called nymphs) damage plants directly by sucking out sap. Indirectly they can also encourage sooty mold and transmit plant viruses.

To discourage whiteflies, avoid applying excess nitrogen or allowing your plants to become water-stressed. This makes the sap more nutritious and can result in greater whitefly reproduction.

Biological control is also effective. Whitefly are prey to lacewings, wasps, and other predatory bugs. Avoid applying insecticides to benefit from the biological control these species provide. Including flowering plants in the landscape will provide whitefly enemies with food and habitat.


Chemicals should be the last line of control in any insect species. Low-impact insecticides, like insecticidal soaps and horticultural oils, can reduce whitefly populations effectively. Read all labels to be sure the product you choose is safe for use on edible crops. When you apply, thoroughly cover the underside of the leaves. Repeat your application frequently, and keep in mind that intense heat and sunlight may cause these products to damage tomato plants.

Whitefly adults are easier to spot than their nymphs. Credit: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Aphids are soft-bodied, sucking insects. In Florida, winged and wingless aphids are all female, born pregnant, and give birth to live young. Some reproduce only 7-10 days after birth! Due to their extremely short lifecycle a few aphids can multiply into an infestation with amazing speed.

The newly born nymphs feed on leaves and blossoms of the plants, causing leaf distortion and even reduced fruiting. The honeydew they excrete encourages sooty mold, as with whiteflies. Also like whiteflies, the winged forms travel between plants and can spread viruses.

Tiny brown bugs on the underside of a green leaf

Aphids found in the underside of a leaf. Credit: UF/IFAS Plant Pathology

Control aphids much as you would whiteflies: keep your plants healthy, protect aphid enemies (like lady beetles), and apply chemicals as a last resort.

Unlike whiteflies, aphids can also be removed by a quick blast from the hose. Remember to focus on the undersides of the leaves, where aphids hide. If new growth is stunted, you may want to trim the plants back to remove the aphids along with the damaged tissue.

Stink Bugs and Leaffooted Bugs

Stinkbugs produce a foul odor when disturbed. Credit: Frank Peairs, Colorado State University, Bugwood.org

Leaffooted bugs can be identified by their "foliaceous hind tibiae." Credit: UF/UFAS

Like aphids and whiteflies, these bugs are sucking insects. Both stink bugs and leaffooted bugs release chemicals that produce a strong, unpleasant smell when they're disturbed. Both insects' lifecycles take about two months to complete. They may not multiply rapidly, but the damage they do is significant.

Stink bugs and leaffooted bugs suck the juices from young fruit. They leave behind diseased and discolored patches as evidence of their feeding. Worse still, the fruit may become infected or distorted as a result.

Both species of bugs are mobile and difficult to control with insecticides. Luckily, both are prey to several species of parasitic flies. Their eggs are also attacked by multiple predators, including tiny parasitic wasps. For this reason, avoid applying insecticides and killing the "good bugs" along with the bad. Instead, remove these pests by hand or with a butterfly net and dispose of them.


Leaf Miner

Leaf miners leave white trails, visible on the upper surface of a leaf. Credit: UF/IFAS Plant Pathology

Vegetable leaf miners (Liriomyza sativae and L. trifolii) are common and easy to spot while scouting for pests. The adult form of a leaf miner is a small black fly, about an eighth of an inch long. Adult females feed briefly on leaves and lay eggs in the process. When these eggs hatch, the larvae eat the leaf from the inside, tunneling through the tissue and leaving white, winding paths visible from the surface. Although tomato fruits remain undamaged, damaged leaves may absorb sunlight less effectively and can become infected.

Leaves with extensive damage should be removed and disposed of to keep leaf miner populations from growing. Fighting on your side against these pests are our native parasitic wasps. These will naturally control leaf miners as long as insecticides don't drive them away. They can be purchased and released in your garden. Horticultural oils are effective as well.

Thrips

Western flower thrips (Frankliniella occidentalis) are common throughout Florida. At less than 1/16th of an inch long, these insects are almost microscopic. Gardeners usually spot the damage thrips cause before the insects themselves. Most species complete their lifecycle in 15-30 days, so early detection is important to prevent infestation.

Leaf and fruit damage caused by thrips. Credit: UF/IFAS Plant Pathology

Thrips (singular: also thrips) are commonly found in flowers and fruits. Adults lay their eggs inside tomato fruits, causing dimples. When these larvae feed on the fruit, the damage is called "flecking." In addition to damaging flowers and fruits, thrips spread several tomato viruses, including tomato spotted-wilt virus.

Much like aphids and whiteflies, thrips have many natural predators. The key to thrips management is encouraging these beneficial insects. Avoid applying insecticides that might kill the predators along with the thrips. If an infestation gets out of hand, insecticidal soaps are effective in reducing the thrips population.

No matter what pests you're battling, the first steps in any pest control routine are prevention, early detection, and proper identification. Daily walkthroughs of your garden, scouting for pests, are key. The sooner you notice a pest problem, the easier it is to manage. Cultural practices, like encouraging beneficial insects, will help you avoid many infestations altogether.

For more information about IPM and pest management, contact your county Extension office.

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