well, it COULD be bud rot, or a small spider inside your bud, or a small infestation of spider mites that will get bigger, or even insulation or a cottonwood-pollen that stuck to your bud. Share a picture and we can help figure it out. bud rot definitely is a risk, as you found it near the brown leaf, but bud rot for me has always started as a dark mass inside the bud, not white. And Powdery mildew, our other favorite fungus, usually doesnt start inside just one bud but all the way up and down where fat buds rub the stem (or white patches on the leaves obviously) But dont start chopping things out until you figure out what it is,every year in my outdoor i find 2-3 spiders that built a home in my buds and were helping them to stay healthy (from moths aphids etc)