Two conditions that cause black spots on tomatoes are late blight and anthracnose. The first disease attacks the leaves of the plant, while the second disease attacks the fruit.
Late blight is a fungal disease that first appears as light or wet spots on the tomato plant leaves. The spots then darken to black, and a fungus might be seen on the underside of the leaf. The disease can be virulent and cool, we weather helps it to spread. It causes the plant to become soft and weak, and it gives it a strong, characteristic odor.
Late blight is best prevented by crop rotation and not rotating tomatoes and potatoes in the same spot year after year. The debris left over from the harvest should be cleaned up thoroughly. During the infection, the plants should be dusted every week or so.
Anthracnose appears as dark, sunken spots on the fruit. The centers of the spots might ooze pink spores. This disease, which is also a fungal disease, thrives in warm, rainy and humid conditions. The best way to avoid this disease is to rotate crops and buy seeds that are resistant. The garden should also not be worked when it's wet because doing so helps the disease spread.