The sudden appearance of damaged or missing tomato plants is a frustrating experience for gardeners. Since the damage occurs overnight, the culprits are primarily nocturnal, hiding during the day and feeding under the cover of darkness. Identifying the specific offender is the first step toward effective protection, as control methods vary widely between insects and mammals. This requires understanding the habits of these nighttime visitors and carefully examining the evidence they leave behind.
Primary Nocturnal Culprits
The most destructive nighttime feeders fall into two main categories: insects and small mammals. Significant insect threats include the larval stages of moths, specifically cutworms and tomato hornworms. Cutworms are plump, smooth-skinned caterpillars that hide beneath the soil or debris during the day. The tomato hornworm, the larva of the sphinx moth, is a much larger, voracious caterpillar that can grow up to four inches long and is perfectly camouflaged against the foliage.
Mollusks like slugs and snails also emerge at night, especially when conditions are damp and cool, to scrape and chew plant tissue. Both leave a distinctive mucous trail as they move across the garden. Small nocturnal mammals and rodents, including raccoons, rats, and mice, are opportunistic feeders that consume ripening tomato fruit. Rats are adept climbers and will scale tomato cages to reach fruit, often causing damage only noticed the following morning.
Damage Patterns and Identification
The specific nature of the plant damage provides the best clue for pinpointing the exact pest responsible. When a young seedling or newly transplanted stem is found completely severed at or just above the soil line, the culprit is almost certainly a cutworm. These larvae wrap around the stem, chew through the tissue, and retreat back into the soil before sunrise.
If the damage involves significant defoliation, where entire leaves or branches are stripped, the tomato hornworm is the likely suspect. These large caterpillars consume massive amounts of foliage. Their presence is confirmed by finding large, dark green, pellet-like droppings, known as frass, on the leaves below the feeding site.
Irregular holes chewed into leaves, especially on lower foliage, combined with shiny, silvery trails across the soil or plant surfaces, points directly to slugs and snails. This mucous trail is the dried slime these mollusks excrete to aid in movement.
When ripe fruit is partially eaten, often with messy, ragged holes, a mammal is responsible. Raccoons and rodents will take bites out of multiple tomatoes, sometimes knocking the fruit from the vine. The key differentiator from insect damage is the size and nature of the bite mark, which is much larger and less precise than the feeding patterns of caterpillars or slugs.
Targeted Control Methods
Protecting young plants from cutworms requires creating a physical barrier around the stem at the soil line. Simple cardboard collars, cut from paper towel rolls or similar material and sunk an inch into the soil, prevent the larva from encircling the plant to cut the stem.
For hornworms, which feed higher up, hand-picking them off the plants at dusk or using a blacklight at night to make them glow is highly effective. For a widespread problem, a biological control using the bacterium Bacillus thuringiensis subspecies kurstaki (Btk) can be sprayed onto the foliage, which is only toxic to caterpillars upon ingestion.
Slugs and snails are best controlled by setting out beer traps, which lure the mollusks to a shallow dish of fermenting liquid where they drown. Alternatively, creating a dry barrier of diatomaceous earth or crushed eggshells around the base of the plants deters them, as the sharp edges damage their soft bodies.
To deter small mammals, the most reliable method is exclusion, such as erecting a secure fence or hardware cloth cage around the tomato patch. Maintaining a clean garden by removing overgrown weeds or low-hanging tomato foliage also removes the dark, sheltered hiding spots favored by rats during the day.