The sudden appearance of white spots on ripening tomatoes can be a source of frustration for any home gardener. These blemishes often suggest a problem with the plant’s health or environment, leading to concern over the edibility of the harvest. Fortunately, the presence of these white areas is usually not a symptom of a systemic disease. The most frequent causes are related to environmental stress or specific pest activity, and understanding the distinct appearance of each guides the gardener toward the correct solution.
White Spots Caused by Sunscald
Sunscald is essentially a sunburn that develops on tomato fruit exposed too rapidly to intense solar radiation and high temperatures. This physiological disorder is common during periods of extreme heat, especially when fruit that was previously sheltered becomes suddenly exposed. The initial symptom is a pale, shiny white or yellowish blotch on the side of the tomato facing the sun. This discoloration occurs because the intense heat and light destroy the pigments in the fruit’s skin cells.
The affected area can be quite large, often covering a significant portion of the fruit’s surface. As the damage progresses, the tissue loses moisture, causing the pale spot to become blistered, wrinkled, and leathery in texture. This dead, bleached tissue is highly susceptible to secondary invasion by rot organisms, such as black mold. The loss of protective foliage from over-pruning or leaf diseases is a frequent trigger.
While the sunscalded portion of the tomato will not ripen properly, the damage is generally superficial and does not affect the interior flesh unless secondary rot has set in. The unaffected portions remain perfectly edible once the damaged patch is cut away.
Pinprick Spots from Insect Feeding
A different type of white spot, often described as a cloudy spot, results from the feeding activity of certain piercing-sucking insects, most notably the Stink Bug. These shield-shaped pests use their needle-like mouthparts to probe the fruit and draw out plant juices. During this feeding process, the insect injects saliva that contains enzymes or toxins into the fruit tissue.
This injection causes the cells immediately beneath the skin to collapse and die, resulting in a small, distinct mark on the surface. On green fruit, the damage appears as a whitish or yellowish spot, often with a tiny, dark pinprick visible at the center where the insect fed. When the tomato is sliced open, the tissue directly under the spot is revealed to be a white, spongy, or corky mass that never develops a normal texture.
These spots are typically smaller than sunscald blemishes and are scattered randomly across the fruit rather than being confined to the sun-facing side. The damage is purely cosmetic and textural; the fruit remains safe to eat, but the spongy texture makes the affected area unappetizing. Stink Bug activity tends to increase from mid-summer onward.
Distinguishing Between Environmental and Pest Damage
Identifying the specific cause requires careful observation of the blemish’s characteristics, including size, location, and internal texture. Sunscald damage presents as a large, continuous patch, often several inches in diameter, centered on the most sun-exposed area of the tomato. The surface of a sunscald patch feels thin, papery, or leathery. In contrast, insect feeding damage appears as multiple small, discrete spots, not restricted to the side facing the sun. The internal texture is the clearest differentiator: sunscald is a surface-level skin issue, while insect feeding results in a noticeable, white, spongy mass of dead tissue just beneath the skin.
Long-Term Prevention and Management
Preventing Sunscald
Preventing sunscald primarily involves maintaining a dense, healthy canopy of foliage to provide natural shade for the developing fruit. Gardeners should avoid excessive or aggressive pruning of tomato plants, as removing too many leaves exposes the fruit to direct, intense sunlight. If plants have lost leaves due to disease or during extreme heat waves, providing temporary shade using a piece of shade cloth is an effective intervention. A shade cloth with a 30% to 40% rating is sufficient to filter out harsh light without hindering plant growth.
Managing Stink Bugs and Other Pests
Managing the pests responsible for pinprick spots requires vigilance, especially since Stink Bugs are elusive and often hide deep within the plant or in nearby weeds. Eliminating weeds and tall grasses surrounding the garden helps to reduce their habitat and overwintering sites. A low-tech method for removal involves shaking the tomato plants vigorously over a bucket of soapy water, causing the insects to drop off for easy collection.
For heavy pest pressure, non-chemical treatments such as insecticidal soap or neem oil can be applied, but they must directly contact the insects to be effective. Prioritizing plant health through proper watering and disease control indirectly prevents both sunscald and pest damage by ensuring the protective foliage remains intact.