What are those yellow weeds?

Weedy fields become very common in a wet spring like we are having.  One of the most striking weeds is Butterweed. Sometimes their yellow flowers appear to blanket a field.  They are a fast growing, early blooming annual that are common in Illinois,  It may also be referred to as cressleaf groundsell, To furtherconfusion it has two scientific names as well.  Formerly called Senicio Glabellus, it is now know as Packera Glabella.  Early Spring weeds in No-till Crop Production  has lots of good pictures of many spring weeds and charts for appropriate controls.  Butterweed can be controlled fairly easily either with chemicals or by tillage.