Anthracnose is caused by a fungus, not by poor soil or a hidden bug. The dark, sunken spots you see on leaves, stems, and fruit come from fungal spores. They move into your plant when the air stays wet. So the anthracnose cause is a living organism. The Colletotrichum fungus is the one behind most cases you will run into.
One pattern gives it away fast. Anthracnose flares right after rainy, humid spells. Then it quiets down once the weather dries out. That timing points straight to a water-spread fungus. A nutrient gap or a pest problem would not track the rain like this. When your spots show up in the same week as a soggy stretch, you can stop hunting for other reasons. The anthracnose cause is sitting in that wet weather, and the rain is what wakes it up.
The biology is wider than one bug. More than one kind of fungus can set it off. But Colletotrichum types cause it most of the time. There are about 340 named kinds in that group. They attack a long list of plants. Beans, tomatoes, peppers, sycamore, dogwood, and many lawn grasses all get their own version. Each kind tends to favor certain plants. That is why the spots look a bit different from one crop to the next, even when the same fungus is at work. You can see the same disease take many shapes across your yard.
It helps to see where this fits in the bigger picture. Fungi cause roughly 90% of all known plant diseases. So a fungal plant disease like this one is the rule, not the exception. Knowing the cause is fungal narrows your whole response. You are dealing with spores, moisture, and timing. You are not dealing with a quick spray-and-forget fix. That single fact saves you from chasing the wrong problem all season.
Anthracnose needs free water on the plant to take hold. Water at the soil line in the morning so your leaves dry before nightfall, and the fungus loses its window.
The spores get around in simple ways. Rain and overhead watering splash them from the soil up onto your low leaves. There they start new infections. From that point your own hands and tools carry them further. Prune a wet, infected plant and then touch a healthy one, and you move the fungus in seconds. This is why anthracnose spreads in clusters. It seems to jump across a bed right after a storm passes through. Sprinklers do the same job as rain, so an overhead system can keep the disease going even in a dry week. The spores also ride on muddy boots and on the blades of unwashed shears.
Since the cause is a wet-weather fungus, your fix should follow the cause. Keep the foliage dry and you cut off the one thing the spores need to grow. Space your plants so air moves between them. Prune crowded growth so the inside of the plant dries out. Avoid working among them while the leaves are still damp from rain or dew. Clear fallen, spotted leaves too. The fungus waits out the season in that debris and comes back the next wet spell.
Do not burn time looking for a single cure. There is no one chemical that erases anthracnose for good. Many gardeners waste a whole season chasing that dream. The lasting answer is dry leaves and clean tools. Manage the moisture and you manage the spread. Wipe your shears with rubbing alcohol between plants so you stop carrying spores by hand. Switch overhead sprinklers for a soaker hose or drip line at the soil. Do that well and the fungus runs out of room to work in your garden. The anthracnose cause never leaves on its own, but you can starve it of the wet leaves it lives on.
Read the full article: Anthracnose Disease: Identify and Stop It
