Winter annual weeds are becoming more prevalent in states to our south. We are starting to see similar changes in the weed spectrum in Wisconsin. The adoption of reduced tillage systems, particularly no-till systems, is probably the primary cause of this weed species/life cycle shift. Others speculate that warmer than normal winters may contribute to the more frequent encounters of winter annuals. This is only a partial explanation as winter annuals normally survive even harsh winters very well. They produce long-chained polymers that drop the freezing point inside the cells to well below freezing (Hall, 1999). Late falls do extend the period of winter annual germination and development, and mild winters probably allow a higher percentage of very small plants to survive. Regardless of the reason, the phenomenon of finding winter annuals more frequently is real.