What are these purple and white spots on the goldenrod leaves? They are caused by a bug, a goldenrod gall midge called Asteromyia carbonifera. The bugs carry a fungus (Botryosphaeria dothidea) that protect their larvae from parasitoids. The female Asteromyia lay eggs and deposit the fungus along with the eggs on the goldenrod leaves. The fungus creates a gall where the eggs can grow unharmed.