Holes in ripening tomatoes are a common frustration for gardeners. Identifying the specific characteristics of the damage is the necessary first step toward protecting the rest of your plants. Proper identification leads quickly to the most effective solution for saving your yield.
The Main Culprits: Insect Pests
The most frequent offenders creating holes in tomato fruit are the larval stages of moths, specifically the Tomato Hornworm and the Tomato Fruitworm. Hornworms, which can grow up to four inches long, consume large, irregular sections of the fruit. They are also capable of completely stripping a plant of its foliage quickly.
The Tomato Fruitworm, also known as the corn earworm, creates smaller, neater entry holes, often near the stem or blossom end. This caterpillar bores directly into the tomato, where it feeds internally, leaving behind tunneling and contamination. Since the worm is protected inside the fruit, the damage may not be visible until the tomato is picked.
Slugs and cutworms are occasional culprits, generally causing damage lower on the plant or on fruit touching the soil. Slugs leave behind ragged holes and a tell-tale slime trail, feeding mostly on the surface. Cutworms are known for severing young seedlings, but they can also chew irregular holes into the sides of low-hanging fruit.
Wildlife and Environmental Causes
Larger pests and physical stresses also cause damage. Small mammals such as squirrels and mice often sample fruit, leaving behind large, ragged bite marks. Squirrels are notorious for taking a few bites out of multiple tomatoes before discarding them. Mice and rats usually feed at night and may leave damage on the upper portions of the fruit.
Birds, particularly crows and jays, create small, shallow pecks in the fruit as they seek moisture during dry periods. This damage often appears as tiny punctures, sometimes in a triangular pattern. These pecks break the skin and invite fungal pathogens and rot.
Environmental conditions can also result in damage that mimics a hole. Rapid changes in soil moisture, such as heavy rain after a dry spell, cause the fruit to swell quickly. This leads to concentric or radial cracking near the stem end. These cracks are open wounds that can easily turn into soft, collapsed spots.
Identifying the Specific Damage Type
To determine the source of the damage, look for clues beyond the hole itself. The presence of frass (insect droppings) indicates caterpillar activity. Hornworm frass is large, dark green, and pellet-shaped, often found on the leaves or the ground beneath the feeding site.
The size and depth of the hole provide another clue. A small, clean entry hole with signs of internal decay points directly to the Tomato Fruitworm. Shallow pecks or triangular marks suggest bird damage, while large, uneven chunks are typically the work of small mammals. Examine the surrounding area for tracks or for the disappearance of entire fruits, which might indicate a larger animal like a raccoon.
The time of day is also a distinguishing factor, as rodents like rats are nocturnal, and squirrels are active during daylight hours. If you suspect hornworms, inspect the plant at night with a blacklight, as the caterpillars fluoresce. Observing which part of the plant is affected—fruit versus leaves—will narrow down the potential culprits.
Immediate Control and Prevention
Immediate Control
Once the culprit is identified, immediate steps can be taken to protect the remaining crop. For hornworms, the most effective action is handpicking the pests off the plant and destroying them. For small mammals and birds, physical exclusion is the best defense, accomplished by covering the plants with a fine-mesh netting or row cover secured to the ground. To address cutworm damage on young plants, create a physical barrier around the stem using a collar made from cardboard or plastic pushed into the soil. For internal feeders like the Tomato Fruitworm, immediately remove and destroy any damaged fruit to prevent the larva from completing its life cycle.
Prevention
Preventative measures will ensure the problem does not recur next season. Consistent, deep watering helps prevent the rapid expansion of fruit that leads to cracking. Introducing beneficial insects, such as parasitic wasps, or applying organic controls like Bacillus thuringiensis (Bt) to the foliage can selectively target and control caterpillar populations.