Probably a pest attack

I use microbes to control gnats and spider mites. Spray both on the plant and the soil. The microbe that I like is Beauvaria bassiana since it works well on both insects and spiders. But I alternate with Metharizium to keep them form adapting. It is slow and doesn't last long. These are microbes normally lives underground and can't survive above ground for too long. You will need to spray a few rounds.