The presence of destructive caterpillars can threaten a bountiful tomato harvest. The term “tomato worms” primarily refers to the Tomato Hornworm, a large larva that can rapidly defoliate plants, although the Tomato Fruitworm is another common and damaging pest. Natural methods focus on preserving the health of the garden ecosystem while effectively removing the culprits. These non-chemical approaches, ranging from simple physical removal to biological controls, ensure your tomatoes are safe for consumption and your garden remains productive. This guide focuses on natural, hands-on, and preventative strategies to manage these pests.
Identifying the Common Tomato Pests
Recognizing the pest attacking your plants is the first step toward effective removal. The Tomato Hornworm (Manduca quinquemaculata) is large, growing up to five inches long with a thick, bright green body that provides remarkable camouflage against the foliage. This caterpillar features eight distinctive white, V-shaped markings along each side, culminating in a dark, horn-like projection at its rear end. The tell-tale sign of its feeding is rapid defoliation, often starting near the top of the plant, along with the presence of large, dark droppings, called frass, on the leaves below.
In contrast, the Tomato Fruitworm (Helicoverpa zea), also known as the corn earworm, is smaller, typically reaching two inches in length. Its color varies, appearing green, brown, pink, or yellow, and it has alternating light and dark stripes running lengthwise down its body. Unlike the hornworm, the fruitworm primarily targets the actual tomatoes, boring a small hole into the fruit, usually near the stem end. This tunneling creates a cavity filled with decay and droppings, rendering the fruit inedible.
Immediate Physical Removal Techniques
The most direct way to protect your tomato plants is through physical removal of the caterpillars. Because of their excellent camouflage, a systematic inspection of the plants is necessary, especially where damage or frass is observed. Focus your search on the upper, inner portions of the plant where the worms prefer to feed and rest.
Handpicking is most successful when the worms are actively feeding, which often occurs early in the morning or late in the evening. For a more efficient nighttime search, a blacklight can be used, as the hornworms’ bodies fluoresce a bright, pale green under this light, making them easy to spot. Wearing gardening gloves can make the process more comfortable.
Once a worm is located and detached, proper disposal ensures it cannot return to the garden. The most effective method is dropping the collected caterpillars into a container of soapy water. The dish soap breaks the surface tension of the water, causing the worms to quickly drown. Alternatively, they can be crushed.
Utilizing Biological and Microbial Controls
For infestations too large for handpicking, or as a preventative measure, biological agents offer a natural solution. Bacillus thuringiensis subspecies kurstaki (Btk) is a naturally occurring soil bacterium effective against caterpillars and safe for other wildlife, beneficial insects, and humans. Btk works as a stomach poison, requiring the caterpillar to ingest the treated foliage to be effective.
Once consumed, the crystalline proteins produced by the Btk paralyze the caterpillar’s digestive system, causing it to stop feeding within hours and die within a few days. The product should be applied thoroughly to all foliage, including the undersides of leaves. It is best sprayed in the late afternoon or evening because sunlight rapidly degrades the bacteria. Reapplication every five to seven days is necessary to maintain coverage, especially after rain, since the product only affects caterpillars that are actively feeding.
Another natural control involves encouraging the presence of the braconid wasp, a tiny beneficial insect that parasitizes the hornworm. The female wasp lays its eggs beneath the caterpillar’s skin, and the larvae feed internally before emerging to spin small, white, rice-like cocoons on the worm’s exterior. If you find a hornworm covered in these cocoons, leave it on the plant, as the worm is already doomed and the emerging wasps will patrol the garden. Ladybugs and green lacewings also offer control by feeding on the newly hatched larvae and eggs.
Cultural Practices for Long-Term Prevention
Long-term management relies on creating a garden environment that deters the adult moths from laying eggs. Companion planting is an effective strategy, utilizing the scents of certain plants to confuse or repel the adult sphinx moths. Planting herbs such as dill, basil, or borage interspersed among your tomato plants can help mask the tomato scent that attracts the moths.
Marigolds are a popular companion plant, as their strong scent is thought to repel a variety of garden pests. Physical barriers offer another preventative layer, especially early in the season when the first generation of moths emerges to lay eggs. Lightweight row covers placed over young plants can physically block the moths from accessing the foliage, though these must be removed once the plants flower to allow for pollination.
Garden sanitation and soil management disrupt the pest’s life cycle. Both the hornworm and fruitworm spend the winter months pupating a few inches below the soil surface. Tilling the garden soil in the late fall, after the harvest is complete, can expose or physically damage the overwintering pupae, significantly reducing the number of adult moths that emerge the following spring.