tomato plants have black spots on the leaves
There are two primary fungus diseases that can produce black spots on tomato plant leaves: Septoria leaf spot and Alternaria leaf spot, also known as early blight. Septoria and Alternaria differ slightly in appearance and prefer slightly different weather climates.
Tomato Spotted Wilt Virus. The tomato spotted wilt virus (TSWV) causes dark brown, purple or black spots on leaves. The spots can spread to the stems, causing cankers and streaks. The foliage begins to wilt once the disease spreads, and the leaves become stiff.
Plants that have been damaged are particularly susceptible to being infected by tomato early blight alternaria. When a plant is infected with Alternaria Alternata, it will normally appear first on the lower leaves of the plant in the form of plant leaf spots that are either brown or black. These tomato leaf spots will eventually migrate to the stem and even the fruit of the tomato.