Answer: I think what you are seeing is the natural breakdown of the organic matter (manure) that you put on your soil. This fungus lives on the decaying organic matter and if you rake the manure around to speed up the breakdown and to incorporate some air, the white fungus will go away. It is possibile that it was too fresh (we call it too hot) and it cooked your bulbs as they tried to sprout. That's why it is important to use only aged manure, not fresh manure. All you need to do is dig the manure into the soil and it will breakdown underground and not be so hot.
Best wishes with your garden!
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