The appearance of damage on your ripening fruit or healthy foliage is frustrating for any gardener. When a tomato plant begins to show signs of distress, successful intervention hinges entirely on accurate identification. A strategy effective against a hungry caterpillar will have no impact on a thirsty squirrel. By adopting a systematic approach to investigating the evidence left behind, you can move quickly to targeted action. Understanding the specific patterns of damage is the first step toward protecting your harvest.
Diagnosing the Damage
The initial step is to become a careful observer, classifying the injury based on its location and pattern. Note whether the feeding occurs on green or ripe fruit, leaves, or the main stems of the plant. Damage appearing as large, ragged holes, particularly on the lower fruit, often suggests a larger mammal or bird is the offender.
Small, superficial chew marks or pinprick-sized spots on the fruit and foliage point toward insect activity. Examine the plant for internal tunneling, which indicates a larva has bored inside the tomato. Look for signs of defoliation, where entire leaves disappear quickly. Small, dark pellets of droppings, known as frass, found on the leaves or the ground beneath the plant are also important clues.
Silvery trails across the soil or plant surfaces are the signatures of slugs and snails. The timing of the damage can also narrow the possibilities; if the damage appears overnight, you are likely dealing with a nocturnal pest. Daytime damage points to creatures active during daylight hours.
Identifying the Culprit
Large, single bites taken out of multiple ripening tomatoes, often leaving the fruit still on the vine, are characteristic of squirrels. These daytime raiders often seem to be seeking water more than a meal, leading them to sample the juiciest part of the fruit and move on. Birds, particularly seeking moisture during hot weather, leave small, shallow pecking marks, usually near the top of the tomato.
Nocturnal mammals, such as rats or raccoons, tend to damage lower-hanging fruit. They may leave larger, messier excavations or drag the fruit away entirely. Among the insects, the tomato hornworm leaves distinct, pellet-like frass and causes massive defoliation almost overnight. These large, green caterpillars cause large, open scars on the fruit surface rather than boring deeply inside.
In contrast, the smaller tomato fruitworm bores a small entry hole, often near the stem end, and tunnels through the interior of the fruit, contaminating it with frass and causing internal rot. Piercing-sucking insects like stink bugs and spider mites cause tiny, pale spots on the leaves and hard, white or yellowish patches just beneath the skin of the fruit. Slugs or snails chew irregular holes in leaves and fruit, preferring to feed in the cool, moist conditions of the evening.
Targeted Management Strategies
Once the culprit is identified, the response should begin with physical exclusion for larger pests. For squirrels and birds, physical barriers like lightweight bird netting draped over the plants or individual cages constructed from hardware cloth are the most reliable long-term solution. Since many animals are searching for water, providing a shallow water source, such as a bird bath, away from your tomato patch can divert their attention. For nocturnal ground pests, a low, solid fence buried a few inches into the soil can deter rats or raccoons.
For caterpillars like the tomato hornworm and fruitworm, hand-picking remains an extremely effective and non-toxic control method. Search for the distinct frass pellets to locate the camouflaged worms above. A biological control agent, Bacillus thuringiensis (Bt), is a naturally occurring soil bacterium that is sprayed onto the foliage. It is toxic only to the larvae of moths and butterflies upon ingestion. Beer traps, consisting of a shallow dish filled with beer sunk into the soil, provide an easy way to eliminate slugs and snails.
Cultural practices play a significant role in pest management and prevention. Maintaining good sanitation by removing damaged fruit and plant debris eliminates hiding spots and food sources for many pests. Avoid overhead watering late in the day, as moist soil conditions favor slugs and snails; instead, water at the base of the plant in the morning. Frequent monitoring of the plant, especially the undersides of leaves where many insects lay eggs, allows for the early removal of pests before they cause significant damage.