Tomato growers may encounter a situation where brown spots suddenly appear on otherwise healthy fruit, which can be quite alarming. What’s going on? In fact, the brown spots on tomato fruit could be caused by diseases, pests, unsuitable environmental conditions, or poor management.
First, let’s talk about diseases. One common disease is late blight, which tends to occur in cool and humid weather. The spots on the fruit are brown or dark brown, irregular in shape, with fuzzy edges, and may start to sink into the flesh as they grow larger. In humid conditions, white mold may appear, particularly on the underside or back of the fruit, and the leaves may first turn deep green, looking water-soaked, before rotting into brown. Another disease is early blight, which appears in hot and humid weather. The spots usually appear near the fruit stem, ranging from brown to dark brown, round in shape, with concentric ring patterns like a target. Eventually, black mold appears, and the surrounding flesh becomes hard. In severe cases, the fruit may crack.
Anthracnose is common during warm, rainy weather. It starts as light brown small spots, which later form round brown or dark brown spots that are slightly sunken, with a deep center and clear edges. There may also be black spots in concentric circles, and in humid conditions, a pink sticky substance might appear. Bacterial spot disease, also known as scab disease, occurs in hot and humid weather. The spots on the fruit are small (2-5 mm), brown to dark brown, slightly raised, and have a rough surface like scabs. There are no obvious rings, and in severe cases, the spots merge, and the flesh becomes hard.
Now, let’s talk about pests. Pests like cotton bollworm and tobacco hornworm larvae burrow into the fruit to feed, causing the area around the holes to turn brown. The flesh becomes damaged, and there may be pest droppings, leading to rot. Often, you can see pest holes and tunnels nearby. Small pests like the tea yellow mite suck the juice from the fruit skin, causing small brown spots to appear. These spots gradually merge into patches, the skin becomes rough and hard, and the fruit loses its luster. In severe cases, the fruit may grow deformed.
Unsuitable environmental conditions can also cause problems. Sunscald occurs when the fruit is exposed to intense sunlight, causing brown, irregular spots on the sunny side of the fruit. It starts as grayish-white or pale yellow, and then turns brown, feeling dry and hard to the touch. This can also lead to rot. If the temperature drops below 10°C, the fruit may freeze, and brown spots will appear. These spots will be irregular, indicating freeze damage, with soft flesh that makes the fruit unappetizing.
Additionally, poor management can lead to issues. If too much nitrogen fertilizer is used, or if there’s a lack of phosphorus, potassium, calcium, or boron, the fruit won’t develop properly, and the skin cells may die, leading to spots. For example, calcium deficiency can cause larger spots from blossom end rot, while boron deficiency may cause brown dead spots on the fruit skin. In terms of watering, if the soil alternates between dry and wet, such as when the soil is dry for a long time and then suddenly watered heavily, the fruit skin and flesh will grow at different rates, causing cracks. When bacteria enter the cracks, brown spots will form, and uneven watering can make blossom end rot worse.
In summary, brown spots on tomato fruit are often caused by diseases, pests, unsuitable environmental conditions, or improper management. By regularly observing the appearance of the spots and the growing conditions, you can identify the cause and take appropriate measures to resolve the issue, ensuring healthy growth for your tomatoes.
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